Health tip: how to avoid infecting yourself with SARS-Cov-2

Being closer to 85 than 80 now, I try to stay in as good physical shape as possible by walking 4.5 miles around a beautiful reservoir within a mile of my home. It takes about 90 minutes, and I usually meet 40 – 100 walkers, runners, joggers, bicyclists, mommies with kids in baby carriages, and today a lady in a motorized wheelchair.

It is the one place where you don’t need a mask (unless you know you are actively infected with the virus in which case you shouldn’t be out there in the first place). Why? Because the virus is spread as droplets as you breathe out, and they don’t hang around in the air very long, and there’s lots of air when you go outside to dilute them. It’s closed spaces and prolonged contact with the same air which causes infection. If you haven’t already done so please look at — it hasn’t been updated since May but you simply can’t do better than this. The examples he cites are convincing (and scary).

Now our skin is crawling with bacteria and viruses. Estimates go as high as 1 trillion (1,000,000,000,000) per human. But they don’t get through your skin. So if you have the pandemic virus on your skin (particularly your hands) it isn’t going to get through the skin to infect you. It will infect you if you put your hand to your nose or your mouth or your eyes, because those are the parts of you which are no barrier to the pandemic infection.

So aside from giving me dirty looks, when people raise their masks to their nose when they see me coming, they’re giving any pandemic viruses on their hands a free ride to their noses and mouths and a much better shot at infecting them.


If the virus makes it from your hand to the mask, and you keep the mask on, the virus stays there (and hopefully stays there rather than moving inside) as you breathe in an out. So you’re not protecting me and you are possibly harming yourselves. So don’t do it.

Put the mask on and keep it on in most other places, walking in crowded places, stores, restaurants, malls. But if you’re out walking in an uncrowded park enjoy yourself.

For those who don’t know, I’m a medical school graduate (Penn). I’m going to run this by two college classmates (both retired med school professors) and if they tell me I’m wrong, I’ll let you know. I’ll let you know even if they tell me I’m right.

Addendum — 10 November — from a retired professor of medicine at Johns Hopkins. The other one is on his farm on the Eastern Shore of Maryland and will respond when he gets back

“I totally agree with you that unless you put your fingers in or around your nose, you aren’t going to get the covid virus from surface contact. Anecdotally, I would predictably get a significant  URI every year after our annual Hematology meeting in December because I am big on shaking hands, which invariably would touch my nose at some point.  I skipped the last two annual meetings and presto, no URIs since.

As for masking outdoors, for the first 6 months, I was assiduous and furious at nonmaskers. Now, I wear a mask outdoors but only when near other people (on sidewalks etc.). I probably don’t need to when socially distanced but do so as a courtesy to others because they are masked. Bottom line, in DC we’ve gone from ~ 50 % masked to 95 % masked. So I want to encourage that.”

Addendum 11 Nov

From the other retired med school professor

    -your exercise regimen is laudatory……..but you failed to state whether you walk clockwise, counterclockwise, or alternate between the two

    -as usual, your medical analysis is well-reasoned… least technically, but as a physician you know the importance of instilling a feeling of comfort and safety in patients (your fellow walkers, etc), so wearing a mask (of any kind) when they approach might better address the “human condition”

Here’s is sort of an engineering analysis of why masks don’t need to be worn in the great (uncrowded) outdoors.

Figure that  the 50 people I pass on the walk are in perhaps 30 groups 20 doubles 10 singletons.  4.5 miles is 23760 feet. so I see a different group every 792 feet.  Now I’m walking at a pace of 90 *60 seconds for 23,760 feet or 4.4 feet per second  — assume they’re walking at the same pace, so every second we move about 9 feet apart (forgetting the 6 feet or more sideways distance) and we’re well out of each other’s airspace in a few seconds.  That is a miniscule dose of the virus when you consider the volume it is being diluted into (and a very short time of exposure).  Here it is very important to read Bromage, because infectivity is not just dose, it’s  dose x time. 

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  • Josh Winslow  On November 9, 2020 at 8:16 pm

    I think part of the recent dirty looks come from the fact that the Governor has mandated mask wearing as of Friday. I’ve been in the same boat as you, not wearing a mask when I go out walking late at night (to avoid people/crowds) but bright line rules are helpful for ensuring compliance where it does actually matter more so I’m begrudgingly doing it now.

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