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Unmasking mask myths

We are living in an era of a viral pandemic, COVID-19, in which viral particles are spread through the air from one person to another. Numerous scientific studies show that if most people even simple cloth face masks while near each other, this dramatically reduced the viral particles in the air, and increases safety. The effect of wearing masks is so effective that in areas where people follow social distancing & mask rules, the incidence of COVID is shrinking.

However, there has been a growing resistance to wearing a mask, fueled by conspiracy theories, pseudoscience, and Russian social media troll farms deliberately spreading misinformation. It now appears that millions of Americans believe that wearing a face mask is unhealthy.

Many of us have met individuals who claimed that face masks either “block oxygen from getting in” or “make us breathe carbon monoxide.”  Both claims are literally impossible, yet widely believed. So if we have a student make such a claim then how can we turn this into a teachable moment?

Face masks


Addressing the carbon monoxide claim

Revisit the equation for cellular respiration. This process is how all cells in our body work – and this process doesn’t produce carbon monoxide!

So if someone makes this claim then ask them “Where, specifically, is this carbon monoxide coming from?”

If they give a vague response ask them to clarify and back up their answer with a source.  If they look into it for even a minute they will quickly see that their claim is impossible.

Addressing the “air can’t get through the mask” claim

Conspiracy theorists try to have it both ways: They claim that the virus particles are so small that they can get through the mask (and supposedly, therefore would make us sick) yet also claim that the oxygen molecules are too large to pass through the mask, so we (supposedly) get low oxygen and brain damage.

The obvious problem is that the virus particle is over 250 times larger than an oxygen molecule!  The covid molecule is 0.125 microns while an O2 molecule is only 0.0005 microns.

Also, to be clear, single viral particles don’t make people sick. The disease is only spread if people inhale multiple exhalation water-virus droplets, each drop let being thousands of times larger than a viral particle, and each drop containing at least many hundreds of viral particles each. And these drops are what the masks are pretty good at filtering.

CoVid-19 coronavirus particle

Image created by Fusion Animation.

Addressing the low amount of oxygen claim

First off, even without a virus, your body automatically adapts to lower levels of oxygen in the air. If that weren’t the case then anyone who visited a high altitude city like Denver, Colorado, would have died!  As we all know, up in Denver the air is thinner, so there are a lot less O2 molecules around. But we adjust, and as long as we don’t play NFL caliber football for an hour, we’re just fine.

The other claim is that these face masks “trap our breath” preventing us from getting oxygen, so that our O2 blood levels fall.  But see for yourself – they don’t do that!

covid Mask blood oxygen level

Photo credit. Dr. Megan Hall

Dr. Megan Hall writes:

Below is me in 4 scenarios. I wore each mask for 5 minutes and checked my oxygen saturation (shown as the percentage below) along with my heart rate (HR, in beats per minute) using noninvasive pulse oximetry. Keep in mind, immediately prior to this, I had been wearing the surgical mask for 5 hours.

No mask: 98%, HR 64
Surgical mask: 98%, HR 68
N95 mask: 99%, HR 69
N95 plus surgical mask (which is how most healthcare providers are wearing masks): 99%, HR 69.

Finally, if “breathing in your own breath is dangerous” then how come it was perfectly safe – and sometimes necessary! – to perform CPR with mouth to mouth resuscitation?

The air that a person exhales has more than enough O2 to keep someone else alive, and there never was any concern about CO (carbon monoxide) or CO2 from our exhalation harming someone else.

How well do masks work?

They don’t need to stop all droplets. COVID is dangerous not because some particles are airborne (thats true for tons of viruses) but because (a) it transmits more easily, and (b) causes more damage.  When we reduce the number of droplets released, then the spread of covid significantly decreases.

Here is a video from Dr. Joe Hanson, from “It’s ok to be smart.” It is an awesome, slow-motion schlieren imaging experiment that demonstrates why masks work.

How Well Do Masks Work? (Schlieren Imaging In Slow Motion!)

References for “How Well Do Masks Work?”


Anatomy of Torso, Arms, and Legs


Torso anatomy

Torso anatomy

Arm anatomy

Arm anatomy

image by Joumana Medlej

Leg anatomy

Leg anatomy

image by Joumana Medlej

From Human Anatomy Fundamentals: Muscles and Other Body Mass


Leg muscles app – Healthline

Learning Standards


6.MS-LS1-3. Construct an argument supported by evidence that the body systems interact to carry out essential functions of life.

6.MS-LS4-2. Construct an argument using anatomical structures to support evolutionary
relationships among and between fossil organisms and modern organisms.

HS-LS4-1. Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence, including molecular,
anatomical, and developmental similarities inherited from a common ancestor
(homologies), seen through fossils and laboratory and field observations.

SAT Subject area test in Biology

Organismal biology: Structure, function, and development of organisms (with emphasis on plants and animals), animal behavior



It is easy to ask “what is the brain, and how does it work?” A much more difficult question is “what is the mind?,” and “what is consciousness?”


Consciousness is “awareness or sentience of internal or external existence”.

Despite centuries of analyses, definitions, and debates by philosophers and scientists, consciousness remains puzzling and controversial. It is “at once the most familiar and most mysterious aspect of our lives”.

Perhaps the only widely agreed notion about the topic is the intuition that it exists.Opinions differ about what exactly needs to be studied and explained as consciousness. Sometimes it is synonymous with ‘the mind’, other times just an aspect of mind. In the past it was one’s “inner life”, the world of introspection, of private thought, imagination and volition.

Today, with modern research into the brain it often includes any kind of experience, cognition, feeling or perception.

There might be different levels or orders of consciousness, or perhaps different kinds of consciousness – or just one kind with different features.

Other questions include whether only humans are conscious or all animals or even the whole universe. The disparate range of research, notions and speculations raises doubts whether the right questions are being asked.
( – Wikipedia, adapted, Consciousness)

Are there levels of consciousness?

Consciousness isn’t binary (It exists, or it doesn’t exist.) Rather, it seems to exist on a smooth continuum from not at all, all the way up to what we humans experience.

There’s no reason to assume that our awareness & consciousness is the highest level – there may be higher levels, or different kids that we can’t imagine.

Image below from A better way to test for consciousness?

levels of consciousness cognitive development

How does this relate to our bodies?  What if we look at consciousness on the level of a person, and then down to smaller biological components?

Or what if we look at this on the level of a person, and then see how this changes when we look at how many people think when they interact?

“The scale problem of consciousness: Human conscious experience does not reflect information from every scale. Only information at a certain coarse-grained scale in the neural system is reflected in consciousness.”

Image from Chang, Acer & Biehl, Martin & Yu, Yen & Kanai, Ryota. (2019). Information Closure Theory of Consciousness.

scale problem of consciousness

The hard problem of consciousness

“The meta-problem of consciousness is (to a first approximation) the problem of explaining why we think that there is a problem of consciousness.”

– Chalmers on the Meta-Problem

The hard problem of consciousness is the problem of explaining how atoms and molecules work together to create a living being – like us! – that actually feels and experiences the world. How does a living person – like us! – experience awareness? How can we feel alive, experience our own thoughts – when we are built out of parts that have no awareness at all?

How the brain works is one thing – that’s the (relatively!) “easy” problem. We already have learned much about the anatomy of the brain and what kind of cells it is made of. We’re learning how information is sent from our eyes, ears, skin, etc. to the brain. We have even begin to learn how the brain mechanically follows the laws of physics to store, recall, and process information.

But how can we humans (and presumably, animals) experience qualia – instances of subjective, conscious experience?

The philosopher David Chalmers is the first to clearly and forcefully make people aware of what an amazingly hard question is, this hard problem of consciousness.

Easy problems are (relatively) easy because all that is required for their solution is to specify a mechanism that can perform the function. That is, regardless of how complex  the phenomena of easy problems may be, they can eventually be understood by following science as we have always known it.

But the hard problem of consciousness will “persist even when the performance of all the relevant functions is explained”.

Chalmers, David (1995). “Facing up to the problem of consciousness”  Journal of Consciousness Studies. 2 (3): 200–219.

We should note that the very existence of this hard problem is controversial. It has been accepted by most philosophers of mind but its existence is disputed others.

Facing Up to the Problem of Consciousness, David J. Chalmers

Moving Forward on the Problem of Consciousness, David J. Chalmers

Consciousness as a State of Matter, Max Tegmark

Panpsychism: You are conscious but so is your coffee mug

Qualia Formalism in the Water Supply: Reflections on The Science of Consciousness 2018


Is consciousness an illusion?

(Text tba)

Has science shown that consciousness is an illusion?

Is Consciousness Real? Scientific American

The ‘me’ illusion: How your brain conjures up your sense of self

The consciousness illusion

There’s No Such Thing as Consciousness, According to Philosopher Daniel Dennett


Physical correlates of consciousness

If consciousness if real, then presumably it correlates to something going on in our brain. What are the physical correlates of consciousness?

The controversial correlates of consciousness, George A. Mashour, Science 04 May 2018:
Vol. 360, Issue 6388, pp. 493-494, DOI: 10.1126/science.aat5616


Neuroscience Readies for a Showdown Over Consciousness Ideas: To make headway on the mystery of consciousness, some researchers are trying a rigorous new way to test competing theories. Philip Ball, 3/6/2019, Quanta Magazine

Neuroscience Readies for a Showdown Over Consciousness Ideas


Visualizing how consciousness might work

Consciousness might be explained by it being an emergent phenomenon,

Analogy – we can’t predict the existence or behavior of oceans from looking at a single molecule of water. Yet when enough liquid water molecules come together, an ocean – with all of its complex behavior – emerges.

Perhaps consciousness is similar. It might emerge from the interplay of dynamics that we already are beginning to learn about.

“Psychologist and neuroscientist Grit Hein and Ernst Fehr from the Department of Economics, University of Zurich teamed up with Yosuke Morishima, Susanne Leiberg, Sunhae Sul and found that the way relevant brain regions communicate with each other is altered depending on the motives driving a specific behavioral choice.”

Hein G, Morishima Y, Leiberg S, Sul S, & Fehr E (2016). The brain’s functional network architecture reveals human motives. Science, 351 (6277), 1074-8 PMI

gif consciousness brain firing 4


Elucidating the Nature of Human Consciousness Through Art: interview with Greg Dunn

gif consciousness brain firing 3

Philosophical zombies

In physics and philosophy, one way to learn about something is to create a gedankenexperiment (“thought experiment.”).

It may be possible to learn more about minds and consciousness by creating philosophical/biological thought experiments. The most well known one is the question of the philosophical zombie:

A philosophical zombie is a hypothetical being who is physically identical to a normal human being, but completely lacks conscious experience. – David Chalmers.

If a philosophical zombie is possible, then conscious experience is independent of physical world.

This image from Masatoshi Yoshida the-hard-problem-of-consciousness

philosophical zombie consciousness


Related articles

Consciousness in Human and non-Human Animals

Possible minds

Consciousness creep Our machines could become self-aware without our knowing it

External articles

What Is Consciousness? Scientists are beginning to unravel a mystery that has long vexed philosophers, By Christof Koch, Scientific American, June 1, 2018

New Scientist articles

What Is Consciousness?

Consciousness, Stanford Encyclopedia of philosophy

Consciousness. Internet Encyclopedia of Philosophy

Articles on consciousness from New Scientist

Why can’t the world’s greatest minds solve the mystery of consciousness? The Guardian (article), UK

Why we need to figure out a theory of consciousness. The Conversation

Photosynthesis GIFs and interactives

Animals don’t make their own food – they have to find food and eat it. Plants, however, are totally different. They actually make their own food!

Organisms that make their own food are called autotrophs or producers. (they mean the same thing.)

Of course, they do need some things to build this food from. They need carbon dioxide gas (CO2)  water (H2O), a few trace minerals, and energy.

Let’s follow the diagram: What is going in to this leaf? What is coming out of it?

Photosynthesis GIF A

And what exactly is a carbohydrate? Just a bunch of sugar molecules connected together into a bigger structure. Let’s see how this works.

This is a sugar molecule. C6H12O6. That means there are 6 Carbon atoms, 12 Hydrogen atoms, and 6 oxygen atoms.

Screen Shot 2020-04-30 at 12.40.57 PM

Plant cells stitch many of these sugars together into bigger structures. They can be called polysaccharides or carbohydrates.

polysaccharides carbohydrate GIF sugars

What are they used for? The plants use them as building blocks. You can see “hemicellulose,” basically a carb, being linked together with other interesting looks carbs.  They keep linking until they build the structure of a leaf, a stem, or as you can see here, a branch.

Lignin–carbohydrate complex (LCC) in wood cell wall Cellulose Tree

From Direct evidence for α ether linkage between lignin and carbohydrates in wood cell walls, Hiroshi Nishimura et al, Scientific Reports volume 8, Article number: 6538 (2018)

Let’s follow the next diagram: Energy enters from sunlight.

We see an organelle with little green stacks absorbing the sunlight. That’s the chloroplast. What comes out of it?

Chemistry Photosynthesis

We see organic molecules – sugars! – come out of the chloroplast. Also O2 (oxygen gas) comes out of it.

Where do they go? They enter another organelle, the mitochondria – the powerhouse of the cell!

This produces ATP, a chemical that stores energy. Everything else in the cell that uses energy? That would use these ATP molecules.


Correct balanced equation of photosynthesis

Here’s an animation of how this works, as a formula:

photosynthesis vs cellular respiration

from the Amoeba sisters

Here you can use an interactive app to control photosynthesis!

   Photosynthesis app (from Molecular Expressions)


And just because you know that you wanted to see this, here you actually see chloroplasts in plant cells!

Chloroplasts in plant cell 6 smaller


Hands-on manipulatives/lab

In this kinesthetic model, students will learn that plants need carbon dioxide, water, and sunlight to carry out photosynthesis.

Using ping pong balls and egg cartons, they will simulate the production of sugar molecules to store energy (photosynthesis), and then break apart these molecules to acquire energy (cellular respiration).

This active simulation makes it easier to remember both processes!

Modelling Photosynthesis with egg cartons

Modeling Photosynthesis and Cellular Respiration

Modelling Photosynthesis and Cellular Respiration PDF handout

Reading on related topic, giant sequoia tree, PDF packet

How do viruses spread? Airborne vs non-airborne

How viruses spread handshake sneeze

How do viruses spread?

Not by individual virus particles

An individual virus particle is unbelievably tiny.

Since they are so lightweight they can float in the air for relatively long distances. So that makes them airborne, right?

Yet these airborne individual virus particles are almost never a problem. Studies show that people are not at risk of being infected by single viral particle.

Why not? We’re likely always inhaling single viral particles here and there. But they quickly break down, or if they persist then our immune system quickly wipes them out.

So if that ain’t the problem then what is? The problem is when we encounter a drop of fluid, or a solid surface, which may have many hundreds or thousands of such viral particles.


Try not to touch people who may be infected! If you do touch someone then wash your hands first.

When it comes to this novel coronavirus (its formal name is SARS-CoV-2) we have to be very careful: An infected person can leave viral particles behind on anything they touch or breathe on.

Infectious material could be left behind on a table, supermarket cart, keypad on an ATM machine, a computer keyboard, on a phone, etc.

A healthy person might touch one of those surfaces, and then touch their face, which then lets those virus particles get in to your airway. That’s a problem, but we can avoid danger: Be careful of what you touch and wash your hands!

Viruses spread exponentially

How does the likelihood of death from any common cause compare to the likelihood of death from something that spreads exponentially? The important difference is that for any other cause of death, that cause is (a) usually not transmissible, and (b) the rate of death stays (more or less) the same over time.

But for deaths caused by a virus the situation is different – (c) it is transmissible from one person to another, and (d) the number of people infected grows exponentially over time.

Animation: Global Deaths Due to Various Causes and COVID-19

Methodology and sources for the animation

Droplets from sneezing and coughing

Sneezing or coughing sends out lots of tiny, snotty water droplets. Each droplet could hold thousands of viral particles. If we inhaled some of these drops then that is enough to make us sick.

Most droplets are short range. The larger ones only go about six feet before they fall to the ground. That’s why it is important to practice social distancing. Stay at least six feet away from people outside of your home.

But read on – with this novel coronavirus (SARS-CoV-2) there is a bit more danger:

viral airborne transmission routes droplets

Image from paper by Jianjian Wei and Yuguo Li. Airborne spread of infectious agents in the indoor environment

Smaller droplets remain in the air longer

The big particles fall quickly, but the small particles float in the air longer – and then they dehydrate (they lose water molecules.) That leaves an even tinier, lighter particle.

These super tiny particles are almost like a gel. Some call these droplet nuclei, or an aerosol, or a bioaerosol. The danger is that these very tiny globs remain airborne much longer, and can travel a further distance. They can float over 20 feet!

That isn’t quite far enough for a virus to technically be called “airborne,” but it still is super dangerous. So if you are indoors – like in a supermarket – the air could become saturated with lots of these tiny droplet nuclei, making the location unsafe.

So when people were saying “this is new coronavirus is bad, but at least it isn’t airborne,” we now know that they were partially incorrect. When indoors this virus is somewhat airborne (6 to 20 feet), and that’s why one needs to avoid supermarkets unless necessary.

Health authorities suggest wearing a mask if you have to do so. Even an imperfect mask is better than none at all.

Airborne transmission virus aerosol droplets

Truly airborne viruses

An airborne virus is one that can float in very tiny aerosol drops, less than 5 microns across, for hours and still remain infectious.

A micron is 0.001 millimeters , or 0.000039 inch.

Its symbol is μm

We now have evidence that this novel coronavirus, SARS-CoV-2, is an airborne virus.

The National Academy of Sciences (NAS) has given a boost to an unsettling idea: that the novel coronavirus can spread through the air—not just through the large droplets emitted in a cough or sneeze. Though current studies aren’t conclusive, “the results of available studies are consistent with aerosolization of virus from normal breathing,”

researchers reported earlier this year in The New England Journal of Medicine that SARS-CoV-2 can float in aerosol droplets—less than 5 microns across—for up to 3 hours, and remain infectious

You may be able to spread coronavirus just by breathing, new report finds, Science, AAAS, Robert F. Service, 4/2/2020

Yes, wearing cloth face masks works!

COVID mask virus transmission coronavirus risk

Cloth masks can help stop the spread of COVID-19, save lives and restore jobs. About 95% of the world lives in countries where the government and leading disease experts both agree that masks are effective at reducing the spread of COVID-19.

Anyone not wearing a cloth mask in public puts everyone at risk of getting infected and they hurt our economy by increasing the chances of a second lockdown.

Why? The U.S. CDC and most experts agree that many infected and contagious people don’t know they’re sick because they don’t have symptoms. Wearing a mask significantly reduces the chances of spreading COVID-19 from you to others.

“Some people have said that covering their faces infringes on their rights, but…it’s about protecting your neighbors…Spreading this disease infringes on your neighbors’ rights.” –Larry Hogan, Governor of Maryland (Republican)

“If everybody’s wearing a mask, it will dramatically reduce the opportunity and possibility of spread.” –Charlie Baker, Governor of Massachusetts (Republican)

Countries that have contained major COVID-19 outbreaks have close to 100% mask usage. An international review of the scientific research on masks by 19 experts (from Stanford, MIT, Oxford, UPenn, Brown, UNC, UCLA, and USF) concluded that:

Near-universal adoption of non-medical masks in public (in conjunction with other measures like test & trace) can reduce effective-R below 1.0 and stop the community spread of the virus.

Laws appear to be highly effective at increasing compliance and slowing or stopping the spread of COVID-19.

There are “34 scientific papers indicating basic masks can be effective in reducing virus transmission in public — and not a single paper that shows clear evidence that they cannot.” –The Washington Post

Read more about the science.



Flight of the aerosol, Ian M Mackay et al. Virology Down Under, 2/9/2020

Simple DIY masks could help flatten the curve. We should all wear them in public.

Face masks

Also see How do viruses spread? Airborne vs non-airborne

Jeremy Howard writes

When historians tally up the many missteps policymakers have made in response to the coronavirus pandemic, the senseless and unscientific push for the general public to avoid wearing masks should be near the top.

The evidence not only fails to support the push, it also contradicts it. It can take a while for official recommendations to catch up with scientific thinking. In this case, such delays might be deadly and economically disastrous.

It’s time to make masks a key part of our fight to contain, then defeat, this pandemic. Masks effective at “flattening the curve” can be made at home with nothing more than a T-shirt and a pair of scissors. We should all wear masks — store-bought or homemade — whenever we’re out in public.

At the height of the HIV crisis, authorities did not tell people to put away condoms. As fatalities from car crashes mounted, no one recommended avoiding seat belts. Yet in a global respiratory pandemic, people who should know better are discouraging Americans from using respiratory protection.

… There are good reasons to believe DIY masks would help a lot. Look at Hong Kong, Mongolia, South Korea and Taiwan, all of which have covid-19 largely under control. They are all near the original epicenter of the pandemic in mainland China, and they have economic ties to China.

Yet none has resorted to a lockdown, such as in China’s Wuhan province. In all of these countries, all of which were hit hard by the SARS respiratory virus outbreak in 2002 and 2003, everyone is wearing masks in public.

George Gao, director general of the Chinese Center for Disease Control and Prevention, stated, “Many people have asymptomatic or presymptomatic infections. If they are wearing face masks, it can prevent droplets that carry the virus from escaping and infecting others.”

My data-focused research institute, fast.ai, has found 34 scientific papers indicating basic masks can be effective in reducing virus transmission in public — and not a single paper that shows clear evidence that they cannot.

Studies have documented definitively that in controlled environments like airplanes, people with masks rarely infect others and rarely become infected themselves, while those without masks more easily infect others or become infected themselves.

Masks don’t have to be complex to be effective. A 2013 paper tested a variety of household materials and found that something as simple as two layers of a cotton T-shirt is highly effective at blocking virus particles of a wide range of sizes.

Oxford University found evidence this month for the effectiveness of simple fabric mouth and nose covers to be so compelling they now are officially acceptable for use in a hospital in many situations. Hospitals running short of N95-rated masks are turning to homemade cloth masks themselves; if it’s good enough to use in a hospital, it’s good enough for a walk to the store.

The reasons the WHO cites for its anti-mask advice are based not on science but on three spurious policy arguments.

First, there are not enough masks for hospital workers.

Second, masks may themselves become contaminated and pass on an infection to the people wearing them.

Third, masks could encourage people to engage in more risky behavior.

None of these is a good reason to avoid wearing a mask in public.

Yes, there is a shortage of manufactured masks, and these should go to hospital workers. But anyone can make a mask at home by cutting up a cotton T-shirt, tying it back together and then washing it at the end of the day. Another approach, recommended by the Hong Kong Consumer Council, involves rigging a simple mask with a paper towel and rubber bands that can be thrown in the trash at the end of each day.

… the idea that masks encourage risky behavior is nonsensical. We give cars anti-lock brakes and seat belts despite the possibility that people might drive more riskily knowing the safety equipment is there. Construction workers wear hard hats even though the hats presumably could encourage less attention to safety. If any risky behavior does occur, societies have the power to make laws against it.

Papers about effectiveness of basic masks #masks4all

About the author – Jeremy Howard is a distinguished research scientist at the University of San Francisco, founding researcher at fast.ai and a member of the World Economic Forum’s Global AI Council.

Simple DIY masks could help flatten the curve. We should all wear them in public.


More reason to wear face masks:

Experts said the choir outbreak is consistent with a growing body of evidence that the virus can be transmitted through aerosols — particles smaller than 5 micrometers that can float in the air for minutes or longer.

The World Health Organization has downplayed the possibility of transmission in aerosols, stressing that the virus is spread through much larger “respiratory droplets,” which are emitted when an infected person coughs or sneezes and quickly fall to a surface.

But a study published March 17 in the New England Journal of Medicine found that when the virus was suspended in a mist under laboratory conditions it remained “viable and infectious” for three hours — though researchers have said that time period would probably be no more than a half-hour in real-world conditions.

Coronavirus choir outbreak


Nell Greenfieldboyce writes

the question of whether or not the coronavirus can be “airborne” is extremely contentious right now — and it’s a question that has real implications for what people should do to avoid getting infected.

… a committee of independent experts convened by the National Academies of Sciences, Engineering, and Medicine has weighed in, in response to a question from the White House Office of Science and Technology Policy about whether the virus “could be spread by conversation in addition to sneeze/cough-induced droplets.”

“Currently available research supports the possibility that SARS-CoV-2 could be spread via bioaerosols generated directly by patients’ exhalation,” says a letter from the committee chair. By bioaerosols, they are referring to fine particles emitted when someone breathes that can be suspended in the air rather than larger droplets produced through coughs and sneezes.

Even if additional research shows that any virus in such tiny particles is viable, researchers still won’t how much of it would need to be inhaled to make someone sick. But the committee experts also caution that uncertainty about all this is almost a given—because there’s currently no respiratory virus for which we know the exact proportion of infections that come from breathing the virus in versus coming into contact with droplets in the air or on surfaces.

“I personally think that transmission by inhalation of virus in the air is happening,” says Linsey Marr, an aerosol scientist at Virginia Tech. But she says so far, health experts have largely discounted the possibility of transmitting this coronavirus in this way.

“From an infection prevention perspective, these things are not 100% black and white. The reason why we say ‘droplet’ versus ‘airborne’ versus ‘contact’ is to give overall guidance on how to manage patients who are expected to be infectious with a specific pathogen,” said Dr. Hanan Balkhy, assistant director-general for antimicrobial resistance at WHO, in an interview with NPR earlier this week.

As an expert who worked to contain an outbreak of the deadly MERS coronavirus in Saudi Arabia, she believes that this new virus should behave similarly to other severe coronaviruses — and that means, unless health-care workers are doing invasive procedures like putting in breathing tubes, the virus is expected to primarily spread through droplets.

Droplets are larger respiratory particles that are 5 to 10 micrometers in size. Those are considered “big,” even though a 5 micrometer particle would still be invisible to the naked eye. Traditionally, those droplets are thought to not travel more than about three feet or so after exhalation. That would mean the virus can only spread to people who get close to an infected person or who touch surfaces or objects that might have become contaminated by these droplets. This is why public health messages urge people to wash their hands and stand at least 6 feet away from other people.

An “airborne” virus, in contrast, has long been considered to be a virus that spreads in exhaled particles that are tiny enough to linger in the air and move with air currents, letting them be breathed in by passersby who then get sick. Measles is a good example of this kind of virus — an exhaled measles pathogen can hang suspended in a room for a couple hours after an infected person leaves.

The reality of aerosol generation, however, is far more complex than this “droplet” versus “airborne” dichotomy would suggest, says Marr. People produce a wide range of different-sized particles of mucus or saliva. These particles get smaller as they evaporate in the air and can travel different distances depending on the surrounding air conditions.

“The way the definitions have been set up, this “droplet” vs “airborne” distinction, was first established in the 1950s or even earlier,” says Marr. “There was a more limited understanding of aerosol science then.”

Even a 5 micrometer droplet can linger in the air. “If the air were perfectly still, it would take a half hour to fall from a height of 6 feet down to the ground. And, of course, the air isn’t perfectly still,” says Marr. “So it can easily be blown around during that time and stay in the air for longer or shorter.”

What’s more, coughs and sneezes create turbulent clouds of gas that can propel respiratory particles forward.

“For symptomatic, violent exhalations including sneezes and coughs, then the droplets can definitely reach much further than the 1 to 2 meter [3 to 6 feet] cutoff,” says Lydia Bourouiba, an infectious disease transmission researcher at MIT, referring to the distance typically cited as safe for avoiding droplet-carried diseases.

In fact, studies show that “given various combinations of an individual patient’s physiology and environmental conditions, such as humidity and temperature, the gas cloud and its payload of pathogen-bearing droplets of all sizes can travel 23 to 27 feet,” she wrote in a recent article published online by the Journal of the American Medical Association.

…. Some of the strongest evidence that an airborne route of transmission might be possible for this virus comes from a report published last month by the New England Journal of Medicine that described mechanically generating aerosols carrying the SARS-CoV-2 virus in the laboratory. It found that the virus in these little aerosols remained viable and infectious throughout the duration of the experiment, which lasted 3 hours.

WHO mentioned this study in its recent review of possible modes of transmission and noted that “this is a high-powered machine that does not reflect normal human cough conditions … this was an experimentally induced aerosol-generating procedure.”

It may have been artificial, says Marr, but “the conditions they used in that laboratory study are actually less favorable for survival compared to the real world. So it’s more likely that the virus can survive under real world conditions.”

Scientists Probe How Coronavirus Might Travel Through The Air

Reference: Turbulent Gas Clouds and Respiratory Pathogen Emissions: Potential Implications for Reducing Transmission of COVID-19

Lydia Bourouiba, JAMA insights, March 26, 2020. doi:10.1001/jama.2020.4756


Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1

March 17, 2020 , DOI: 10.1056/NEJMc2004973

A novel human coronavirus that is now named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (formerly called HCoV-19) emerged in Wuhan, China, in late 2019 and is now causing a pandemic. We analyzed the aerosol and surface stability of SARS-CoV-2 and compared it with SARS-CoV-1, the most closely related human coronavirus.

… We found that the stability of SARS-CoV-2 was similar to that of SARS-CoV-1 under the experimental circumstances tested. This indicates that differences in the epidemiologic characteristics of these viruses probably arise from other factors, including high viral loads in the upper respiratory tract and the potential for persons infected with SARS-CoV-2 to shed and transmit the virus while asymptomatic.

Our results indicate that aerosol and fomite transmission of SARS-CoV-2 is plausible, since the virus can remain viable and infectious in aerosols for hours and on surfaces up to days (depending on the inoculum shed).

These findings echo those with SARS-CoV-1, in which these forms of transmission were associated with nosocomial spread and super-spreading events, and they provide information for pandemic mitigation efforts.

Neeltje van Doremalen, Ph.D., Trenton Bushmaker, B.Sc.
National Institute of Allergy and Infectious Diseases, Hamilton, MT

Dylan H. Morris, M.Phil.,  Princeton University, Princeton, NJ, Myndi G. Holbrook, B.Sc.
National Institute of Allergy and Infectious Diseases, Hamilton, MT

Amandine Gamble, Ph.D.
University of California, Los Angeles, Los Angeles, CA

Brandi N. Williamson, M.P.H.
National Institute of Allergy and Infectious Diseases, Hamilton, MT

Azaibi Tamin, Ph.D., Jennifer L. Harcourt, Ph.D.
Natalie J. Thornburg, Ph.D., Susan I. Gerber, M.D.
Centers for Disease Control and Prevention, Atlanta, GA

James O. Lloyd-Smith, Ph.D.
University of California, Los Angeles, Los Angeles, CA, Bethesda, MD

Emmie de Wit, Ph.D., Vincent J. Munster, Ph.D.
National Institute of Allergy and Infectious Diseases, Hamilton, MT

Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1



Preparing lessons in case schools close for coronavirus

Be Prepared Preparation

Due to the likely imminent arrival of coronavirus outbreaks in America, many school districts are preparing to fight the pandemic with the most effective tool: social distancing. This may include cancelling school, and other public events, for up to 2 weeks in affected areas.

As such, teachers may be asked to prepare 2 weeks worth of lessons for students to do at home as stand alone work. How do we efficiently prepare for this? I have been uploading resources to my website and creating worksheets based on them. In a pinch I could email our students 2 weeks worth of worksheets in PDF format, and print out packets for students with little or no internet access.

Teachers can supplement the work they assign  by creating a YouTube channel with daily mini-lectures. Students could listen & ask questions from their homes.

Teachers of course don’t need their own website. They can use any of their favorite science websites, such as The Physics Classroom.

However, we shouldn’t need something like the coronavirus to begin preparing. It is just good practice for teachers to create a library of ready-to-go, self-contained lesson plans for each topic. Instead of waiting for an emergency, make this part of your weekly schedule: Each week pick your best lesson, and write a self-contained worksheet for it.

As you create handouts (whether destined for PDF or paper) please think about readability, and about students who are slow readers or who have IEPs:

  • Have a brief, clear introduction so the student knows what we are learning and why. See below for details.

  • Use a large enough font.

  • Use double-spacing.

  • Have some space between each section.

  • Break long paragraphs into a smaller paragraphs.

  • Add a color graphic to help explain the concept in each section.

A packed page is a poorly-designed page. Trying to shove a class onto just a page or two is especially irrelevant since we are no longer limited by paper. Students can view as many pages as we need on their PCs, tablets, or phones.

Writing a brief, clear introduction

* Content objective:

Briefly discuss what we are learning, and/or why we are learning this. This may involve teaching new ideas, procedures, or skills.

* Vocabulary objective – What are the critical words in this lesson?

These include not only new terms that you introduce, but supposedly “common” words that one assumes the students “already know.” (The problem is that many students don’t always know what these terms means. Please click the link for more information.)

Tier II vocabulary words: High frequency words used across content areas. They are key to understanding directions, understanding relationships, and for making inferences.

Tier III vocabulary words: Low frequency, domain specific terms.

* Build on what we already know.

Very few lessons start completely from scratch. Most will include some vocabulary & scientific concepts that were learned in earlier grades. So in this section of your introduction, briefly make connections to prior concepts.

How are you preparing for this?


Reliable sources of information

CDC: Centers for Disease Control – Coronavirus Disease 2019 (COVID-19)

Massachusetts Department of Public Health

US FDA Food and Drug Administration Coronavirus Disease 2019

Coronavirus disease: Myth busters – WHO World Health Organization

How to deal with a viral pandemic

What is a pandemic?

A pandemic is an epidemic occurring on a scale which crosses international boundaries, usually affecting a large number of people. Pandemics can also occur in important agricultural organisms (livestock, crop plants, fish, tree species) or in other organisms.

continuum pandemic phases CDC

from The Continuum of Pandemic Phases, CDC

The World Health Organization (WHO) has a classification – starts with the virus mostly infecting animals, with a few cases where animals infect people, then moves through the stage where the virus begins to spread directly between people, and ends with a pandemic when infections from the new virus have spread worldwide.

A disease is not a pandemic merely because it is widespread or kills many people; it must also be infectious. For instance, cancer is responsible for many deaths but is not a pandemic because the disease is not infectious or contagious.

(Intro adapted from Wikipedia article, Pandemic)

Viruses spread exponentially

How does the likelihood of death from any common cause compare to the likelihood of death from something that spreads exponentially? The important difference is that for any other cause of death, that cause is (a) usually not transmissible, and (b) the rate of death stays (more or less) the same over time.

But for deaths caused by a virus the situation is different – (c) it is transmissible from one person to another, and (d) the number of people infected grows exponentially over time.

Animation: Global Deaths Due to Various Causes and COVID-19

Methodology and sources for the animation

How would we respond to a pandemic?

What happens if a pandemic hits? Jon Evans, Techcrunch, 2/23/2020

Don’t get all disaster-movie here. Some people seem to have the notion that a pandemic will mean shutting down borders, building walls, canceling all air travel and quarantining entire nations indefinitely. That is incorrect. Containment attempts can slow down an outbreak and buy time to prepare, but if a pandemic hits, by definition, containment has failed… [so] the focus will switch from containment to mitigation: slowing down how fast the virus spreads through a population in which it has taken root.

Mitigation can occur via individual measures, such as frequent hand washing, and collective measures, such as “social distancing” — cancellations of mass events, closures, adopting remote work and remote education wherever possible, and so forth.

The slower the pandemic moves, the smoother the demands on health-care systems will be; the less risk those systems will have of becoming overloaded; the more they can learn about how best to treat the virus; and the greater the number of people who may ultimately benefit from a vaccine, if one is developed.

How dangerous is the Coronavirus (COVID-19) pandemic?


Pandemic viral symptons iceberg analogy

How should we respond to a pandemic?

Past Time to Tell the Public: “It Will Probably Go Pandemic, and We Should All Prepare Now” by Jody Lanard and Peter M. Sandman

1. Tell friends and family to try to get ahead on their medical prescriptions if they can, in case of very predictable supply chain disruptions, and so they won’t have to go out to the pharmacy at a time when there may be long lines of sick people. This helps them in a practical sense, but it also makes them visualize – often for the first time – how a pandemic may impact them in their everyday lives, even if they don’t actually catch COVID-19….

2. We also recommend that people might want to slowly (so no one will accuse them of panic-buying) start to stock up on enough non-perishable food to last their households through several weeks of social distancing at home during an intense wave of transmission in their community. This too seems to get through emotionally, as well as being useful logistically.

3. Three other recommendations that we feel have gone over well with our friends and acquaintances: Suggesting practical organizational things they and their organizations can do to get ready, such as cross-training to mitigate absenteeism. Suggesting that people make plans for childcare when they are sick, or when their child is sick.

4. Right now, today, start practicing not touching your face when you are out and about! You probably won’t be able to do it perfectly, but you can greatly reduce the frequency of potential self-inoculation. …

How should we respond to a pandemic?

Josh Michaud, Associate Director Global Health at Kaiser Family Foundation, John Hopkins School of Advanced International Studies, writes:

CDC guidance urges flexibility in implementing mitigation measures, and continual re-assessment of their effectiveness as new information comes in. A “targeted, layered” approach that addresses current circumstances is the best practice. The ultimate goal of such measures is to reduce the intensity of an outbreak, flattening out the epidemic curve and therefore reducing strain on the health system, and on social economic well-being (see this graphic representation).

community mitigation for viral pandemic outbreak graph

With community transmission of #COVID19 in multiple countries it appears that containment of the virus in China will not happen (this outcome was not unexpected). Emphasis in many places could turn from containment to “mitigation”. What does mitigation mean?

First, to be clear: it’s not either/or, because containment efforts and mitigation efforts encompass a spectrum of activities, are complementary and can occur at the same time.

Still, we can contrast their goals: containment is meant to halt transmission, while mitigation is meant to reduce negative impacts of transmission.

For the U.S., CDC has long had recommendations for how communities can use mitigation to address pandemic influenza. A revision to this guidance came in 2017, incorporating lessons learned from the 2009 H1N1 influenza pandemic.

“Community Mitigation Guidelines to Prevent Pandemic Influenza — United States, 2017”

Not all guidance from pandemic influenza is applicable to #COVID19 because the epidemiology and circumstances differ, but countries face similar challenges with both.

For example, both are highly transmissible, and in both cases we have no specific countermeasures available at first (e.g. vaccines). Containment is difficult if not impossible in both cases.

The 2009 H1N1 pandemic is often remembered as being “mild”, but there was a quite a significant health impact: an estimated 43-89 million people in the US were infected and 12,000 people died between Apr2009-Apr2010.

CDC talks about mitigation in three buckets: 1) individuals behaviors (hand hygiene, staying at home, avoiding ill people); 2) “social distancing” (closing schools and public gatherings, and 3) environmental mitigation (surface cleaning efforts). Let’s focus in 1 and 2.

Encouraging better individual hygiene behaviors is cornerstone of mitigation. Good hand hygiene (wash those hands!), and voluntary home isolation when ill (and even home quarantine when potentially exposed) are recommended.

Many studies show the effectiveness of hand hygiene; one study on H1N1 from Egypt highlighted by CDC showed 47% fewer cases of influenza occurred after twice-daily hand washing and health hygiene instruction was provided in elementary schools.

Studies of the US public during H1N1 found that people actually did change their hygiene behaviors: in one survey 59% of Americans reported washing hands more frequently and 25% said they avoided public places like sporting events, malls, and public transportation.

CDC guidelines also support social distancing in some cases, including school closures, canceling public gatherings, and workplace closures/telework.

During H1N1, CDC recommended communities with confirmed cases consider closing child care facilities and schools. From Aug–Dec 2009, communities in 46 states implemented 812 dismissals (in a single school or all schools in a district), affecting 1,947 schools.

This number of schools represented 0.7% and 3.3% of all urban and rural schools, respectively, in the U.S. Evidence from TX indicated school closures there reduced acute respiratory illness in households with school-age children by 45%–72%.

Interestingly, surveys of parents whose children were affected by school closures found strong support for, and belief in the effectiveness of these measures: 90% of parents agreed with dismissal decisions, and 85% believed dismissals reduced transmission.

Even so, closing schools was disruptive, and a systematic review of US school closures during H1N1 was not able to determine whether the benefits outweighed the cost in this “mild” epidemic, though they did recommend such measures during a “severe” pandemic.

CDC guidelines also note there are practical obstacles to asking people to stay home from school and work: in 2009 a major difficulty was that many people did not have access to paid leave, and therefore had a hard time following guidance.

Another challenge for mitigation in the U.S. is that while CDC can offer recommendations and guidance, implementation of these policies mostly occurs at local district, county, & state levels. This can lead to a patchwork of different mitigation approaches across locations.
A recent publication looked at US local health department decision-making around social distancing during outbreaks, and concluded resources available and actions implemented are inconsistent and unpredictable across the country. https://journals-sagepub-com.proxy1.library.jhu.edu/doi/pdf/10.1177/0033354918819755

CDC guidance urges flexibility in implementing mitigation measures, and continual re-assessment of their effectiveness as new information comes in. A “targeted, layered” approach that addresses current circumstances is the best practice.

The ultimate goal of such measures is to reduce the intensity of an outbreak, flattening out the epidemic curve and therefore reducing strain on the health system, and on social economic well-being (see this graphic representation).

Reliable sources of information

CDC: Centers for Disease Control – Coronavirus Disease 2019 (COVID-19)

Massachusetts Department of Public Health

US FDA Food and Drug Administration Coronavirus Disease 2019

Coronavirus disease: Myth busters – WHO World Health Organization


The Math and Biology of Beauty: Averages and Symmetry

Aesthetic judgements of physical attractiveness – beauty – are not arbitrary. Scientific studies show that they are are related to biology and healthy, which is often manifested as facial symmetry.

In physical attractiveness studies, “averageness” describes the physical beauty that results from averaging the facial features of people of the same gender and approximately the same age. This is often called the “averageness-effect.”

Studies use photographic overlays of human faces, in which images are morphed together.

The term “average” here is a mathematical definition = arithmetic mean, = the sum of a collection of numbers divided by the count of numbers in the collection.

It turns out that an averaged face is not unremarkable, but is, in fact, quite good looking.

Averageness Face Beauty

Image from Koinophilia and human facial attractiveness, Aishwariya Iyengar et al.

Koinophilia and human facial attractiveness, April 2015, Volume 20, Issue 4, pp 311–319

Nor is averageness typical in the sense of common or frequently occurring in the population, though it appears familiar, and is typical in the sense that it is a good example of a face that is representative of the category of faces.

The evolutionary explanation for averageness is koinophilia: animals seek mates with average features, because extreme or uncommon features indicate disadvantageous mutations.


FaceResearch.org – Make Your Own Average


Note (1) Grammer, K.; Thornhill, R. (October 1994). “Human (Homo sapiens) facial attractiveness and sexual selection: the role of symmetry and averageness”. Journal of Comparative Psychology. 108 (3): 233–42. doi:10.1037/0735-7036.108.3.233. PMID 7924253. Retrieved 4 May 2019.

Rhodes, Gillian; Zebrowitz, Leslie A. (2002). Facial Attractiveness: Evolutionary, Cognitive, and Social Perspectives. Ablex. ISBN 978-1-56750-636-5.

Jones, B. C., Little, A. C., Tiddeman, B. P., Burt, D. M., & Perrett, D. I. (2001). Facial symmetry and judgements of apparent health Support for a “‘ good genes ’” explanation of the attractiveness – symmetry relationship, 22, 417–429.

Alison Pearce Stevens writes “Research shows that people with more symmetrical faces don’t just look nice. They also tend to be healthier than asymmetrical people. Genes provide the instructions for how a cell is to perform. All people have the same number of genes. But people with more average faces tend to have a greater diversity in the genes they are born with. And that, research has shown, can lead to a stronger immune system and better health.” What makes a pretty face? Science News for Students

Medical Daily: The Science Of Attraction: Men Perceive Women With Average, Youthful Facial Features As Beautiful


Iglesias-Julios M, Munoz-Reyes JA, Pita M et al. Facial Features: What Women Perceive as Attractive and What Men Consider Attractive. PLoS ONE. 2015.

Farmer H, McKay R, Tsakiris M. Trust in Me: Trustworthy Others Are Seen as More Physically Similar to the Self. Psychological Science. 2013.

Coetzee V, Keckp S, Kivleniece I et al. Facial attractiveness is related to women’s cortisol and body fat, but not with immune responsiveness. Biology Letters. 2013.

Clarifying codon wheel usage

A student is told to use a “codon wheel” to help with protein translation. What codons go with which resulting amino acid? Here I saw students come to different conclusions because many infographics were not distinctly labeled.

Some students thought that every codon wheel lets us input 3 DNA nucleotides.
Others thought that it let us input 3 mRNAs.
While others thought that it let us input the 3 anticodons on the tRNA molecule.

In other words, many students failed at step 1 because the main idea was not labeled clearly.

In this example (click link) we see mRNA codon wheel.  If we input mRNA sequence then it tells us the amino acid that will be the eventual output from the translation process.

Why mention this? Because there are also tRNA codon wheels, and even DNA codon wheels! Each of these wheels can be fine – but only when we know for certain which one we are using.

Codon Wheel

Let’s follow an example through, step by step.

For the following image, the original DNA sequence must be:


The corresponding mRNA sequence is


The anticodon sequence for the tRNAs is


The amino acids carried by these tRNAS would be

Met Ala Ser

mRNA to tRNA translation step by step

This image from ATDBio Ltd., Transcription Translation and Replication