F*ck the virus.
March 14, 2020 6:08 PM   Subscribe

this is paywalled fyi
posted by OHenryPacey at 6:14 PM on March 14, 2020

Non-paywalled: Science Friday segment (28m) on how and why soap works, with a brief summary on the webpage and extended reading links too.
posted by hippybear at 6:37 PM on March 14, 2020 [2 favorites]

Also not pay-walled is this awesome simulation of why social distancing works.
posted by straight at 6:40 PM on March 14, 2020 [11 favorites]

Just to summarize, soap works by two mechanisms:

1. Soap permits the dirt and oils on your skin — which serve to hold microbes — to become more water-soluble, enabling it all to be washed away.

2. Soap can also break apart and destroy the lipid bilayer of microbe cells, themselves.

The first mechanism simply removes the microbes from your hands. This is, by far, the greatest contributor of soap’s effectiveness in preventing the spread of germs.

The second mechanism destroys microbes. And while sone of this is occurring when you wash your hands, it is not the greater contributor to soap’s effectiveness. Mainly because you do not have soapy water in contact with your hands for a long enough time for this effect to become very large.

Incidentally, this is why washing your hands is by far the best method of preventing germ transfer. You’re not actually trying to destroy the microbes, but just getting them off of you. In contrast, hand sanitizers are less effective because they require significant wetting of the skin and prolonged contact to be able to effectively destroy germs.

Finally, studies have shown that surface disinfectants like chlorine solutions (e.g., diluted bleach) can evaporate before they’ve done all their work. So it’s important to let surfaces remain wet so the disinfectant can be effective (i.e., don’t dry the surface immediately).
posted by darkstar at 6:51 PM on March 14, 2020 [12 favorites]

Also, because there are a lot of artisanal hand “sanitizer” recipes made from essential oils, etc., floating around in the Internet, here is the link to the WHO-recommended hand sanitizer recipes.


Please note that alcohol hand sanitizers must have at least 60% alcohol. Vodka will not do it (80 proof spirits being only 40% alcohol). Everclear is 95% alcohol and can be used, such as in the WHO-recommended formulation.

Non-alcohol sanitizers (e.g. benzalkonium) are much less effective against Covid-19 and may not provide significant effect against the virus.

Very effective sanitizing solutions can be made from bleach. The CDC has provided guidelines here:


Please note the different uses for strong and mild dilutions.

Stay safe, y’all!

(Disclaimer: IANAD or epidemiologist. I’m a biochemist with ten years experience working in community development in remote, undeveloped areas that required using these sorts of sanitization methods.)
posted by darkstar at 7:00 PM on March 14, 2020 [21 favorites]

“Wash your hands like you’ve been chopping jalapeños and you need to change your contacts.”
posted by puffyn at 7:14 PM on March 14, 2020 [23 favorites]

“Wash your hands like you’ve been chopping jalapeños and you need to change your contacts.”
Endorsed by Dr. Bonnie Henry!
(She was on the front lines of SARS in Toronto in 2003; I trust that she knows what she's talking about.)
posted by invokeuse at 7:27 PM on March 14, 2020 [3 favorites]

“Wash your hands like you’ve been chopping jalapeños and you need to change your contacts.”

You could probably teach yourself not to rub yours eyes buy using a jalepeno based moisturizer.
posted by srboisvert at 7:36 PM on March 14, 2020 [9 favorites]

Another non-paywalled link about soap vs. coronavirus from chemistry professor Pall Thordarson at The Guardian.
posted by mbrubeck at 7:46 PM on March 14, 2020

This seems like a good place to ask the question my little group has wondered about: Are all soaps created equal? That is, is anything labeled "soap" good for our anti-viral purposes?
posted by bryon at 10:00 PM on March 14, 2020

My understanding is that the anti-bacterial soaps don't do any good because even in a 20 second wash you won't be using it long enough for the other ingredients to really work. It's the lifting of the dirt layer off the skin which is important and all soaps do this.
posted by hippybear at 10:20 PM on March 14, 2020 [1 favorite]

People have been trying to pick toothpastes, soaps & shampoos without SLS, SDS and SLES (Sodium Lauryl Sulfate and Sodium Laureth Sulfate), but I've seen claims that it helps the antiviral properties of soap, but all the papers I've found are about slightly different uses for humans. Any microbiologists care to comment?
posted by ASCII Costanza head at 10:29 PM on March 14, 2020

That is, is anything labeled "soap" good for our anti-viral purposes?
My hunch is yes. Anything with the "soap" label should work how darkstar described above. There are different soap molecules out there, but as far as I know the differences don't affect the mechanism by which they clean.

People have been trying to pick toothpastes, soaps & shampoos without SLS, SDS and SLES
I'm one of these people. I buy reduced-sulfate shampoos because I have found anecdotally that it reduces hair frizz. SLS and SDS have a similar structure to soap molecules (which I take to be the salts of fatty acids), so I don't find it particularly surprising that they have some anti-viral properties. The paper you linked basically says that SLS and SDS work by mechanism 2 described by darkstar above when applied topically.

(Source: worked on a project involving surfactants once and did too much background reading)
posted by invokeuse at 10:40 PM on March 14, 2020

Just a reminder

posted by Barbara Spitzer at 3:44 AM on March 15, 2020

Possibly dumb question that seems appropriate here (and I'm sure ask.me has had enough of possibly dumb COVID questions...)

With all the handwashing, even with cool water, my hands are dry as a desert right now. If I use lotion, am I undoing all the good work I've done washing my hands (by making them stickier for a bit while the lotion soaks in)?
posted by invincible summer at 8:12 AM on March 15, 2020

I'm going to say that it's all about where you are when you're doing that. If you're in your home and your home is (as far as you know) not a virus-laden location, then you're fine with the lotion and the waiting for it to soak in. If you're putting the lotion on in your car before you walk into a grocery store, then probably not so much.

It's the surfaces you touch outside your home which are the problem and you should definitely wash hands and wipe down doorknobs when you come home from elsewhere, and keep your home a place of refuge.
posted by hippybear at 8:23 AM on March 15, 2020 [2 favorites]

Don’t just wash your hands to prevent coronavirus. Moisturize them, too (WaPo).
Johns and Shapiro confirmed that moisturizing hands does not increase the likelihood of picking up or spreading germs, especially if the hands are clean. Moisturizing hands does reduce microbial shedding from the skin and is part of good hand hygiene, which will protect people from picking up viruses and reduce the likelihood of transmission.

Johns recommends that people apply a thick, emollient moisturizer in ointment form — such as Aquaphor Healing Ointment, rather than relying on creams and lotions, which can have alcohol and cause further drying. Shapiro recommends selecting a soap or sanitizer with an emollient and avoiding perfumes and dyes, as they can further irritate skin. Soaps and sanitizers with moisturizers can be just as effective, though Shapiro says hand sanitizers should have at least 60 percent alcohol.

“Lotion doesn’t need to be a constant thing to be effective,” said Preeti Malani, an infectious-disease doctor and chief health officer at the University of Michigan. And it doesn’t need to be expensive: Drugstore brands such as Vaseline and Aquaphor can work well. Moisturizing lotions work by locking in existing moisture, so the ideal time to apply them is after washing, when the skin is hydrated.
posted by mbrubeck at 9:48 AM on March 15, 2020 [7 favorites]

That is, is anything labeled "soap" good for our anti-viral purposes?

And do the products that seem to go out of their way to carefully NOT say the word "soap" any good for this purpose? Just in my bathroom I have a "daily moisturizing body wash" and a couple of spare bars of Ivory. The Ivory says "99.44% pure, clean, and simple" but nowhere on the entire package does the word "soap" appear. My everyday product of choice has always been Dr. Bronners, which now that I'm watching for it, seems to be the only one to actually use the word.
posted by ctmf at 4:31 PM on March 15, 2020 [1 favorite]

Soap, in the technical sense, is the result of saponifying (reacting with an alkali) some kind of fat or oil. The result is usually a sodium or potassium salt of tallow, coconut oil, palm oil, olive oil, etc. These compounds are surfactants, that help dirt and oil dissolve in water.

You can tell if a substance is a soap because the ingredients will list potassium cocoate, or sodium tallowate, or sodium palmate, for example. Ivory contains these last two, and is therefore a soap. They just don’t use the word on their labeling anymore.

In contrast, the technical category of detergents includes surfactants that are not the result of saponification of fats or oils. There are different categories of detergents (anionic sulfonates, cationic quaternary ammonium salts, etc.), but we usually encounter them in household cleaning supplies.

Detergents perform the same function of soap in making dirt and oils more water-soluble, so they can be removed from a surface. But some detergents are harsher to skin, so they’re not as nice for hand washing.

Dr. Bronner’s and similar Castile soaps are called “Castile” (i.e., made in the Castilian tradition) to signal that they are made from vegetable oils, and do not have harsh additives. Traditionally, olive oil was the plant oil used, but modern Castile soaps use palm oil, coconut oil, and others. Dr. Bronner’s uses coconut oil for its saponification.

One of the many cool things about the saponification process is that a chemical byproduct is glycerine. The presence of glycerine in the soap — left over from the saponification process — provides an emollient effect on the skin when it’s used.

This concludes “Soap Facts”.
posted by darkstar at 5:32 PM on March 15, 2020 [16 favorites]

Do the surfactants in detergent wipes have any anti-viral effect when used on hard surfaces? I wiped all my light switches, door handles and keyboards with Dettol wipes last night but I've no idea if that achieved anything or not.
posted by Paul Slade at 1:05 AM on March 16, 2020

Not sure to what degree.

Detergents would disrupt the lipid bilayer of the virus. But I don’t know the appropriate concentration or contact time that would be necessary for detergents — and particularly that specific detergent — to be effective as a virucide.

I’m using the strong dilution of bleach (1:10 dilution, see CDC link above) in a spray bottle for disinfecting my countertop surfaces that are not reactive to or damaged by bleach.

(Also, I checked my Dr. Bronner’s...the label lists coconut oil as the main oil used, but also includes jojoba, hemp and olive oils.)
posted by darkstar at 8:18 AM on March 16, 2020 [1 favorite]

@Pall Thordarson:

Here is a threadreader version of his twitter thread that led to the Guardian article. With pictures.
posted by indianbadger1 at 8:26 AM on March 16, 2020

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