Plain Old Soap: The Best Disinfectant For Coronaviruses

Why does soap work so well on SARS-CoV-2?, Virology Down Under, Ian M Mackay, PhD (EIC), 9 March 2020

Below is a diagram of a coronavirus, specifically a mouse hepatitis coronavirus.
Source: SARS-CoV-2 and the lessons we have to learn from it, Edward Nirenberg.

Why does soap work so well on the coronavirus and on most viruses? Because soap is made with fat. And like dissolves like:

The soap dissolves the fat membrane [lipid bilayer, in grey in above diagram] and the virus falls apart like a house of cards and “dies”, or rather, we should say it becomes inactive as viruses aren’t really alive.

Disinfectants or liquids, wipes, gels and creams containing alcohol (and soap) have similar effects but are not really quite as good as normal soap. Apart from the alcohol and soap, the “antibacterial agents” in these products don’t affect the virus structure much at all. Consequently, many antibacterial products are basically just an expensive version of soap in terms of how they act on viruses. Soap is the best but alcohol wipes are good when soap is not practical or handy (e.g. office receptions).

About alcohol, he says:

Alcohol does also dissolve the lipid membrane [but] you need a fairly high concentration (maybe +60%) of the alcohol to get a rapid dissolution of the virus. Vodka or whiskey (usually 40% ethanol), will not dissolve the virus as quickly. Overall alcohol is not quite as good as soap.

What do you do with this soap? You wash your hands:

So when you touch say a steel surface with a virus particle on it, it will stick to your skin and hence get transferred onto your hands. But you are not (yet) infected. If you touch your face though, the virus can get transferred from your hands and on to your face.

And now the virus is dangerously close to the airways and the mucus type membranes in and around your mouth and eyes. So the virus can get in…and voila! You are infected (that is unless your immune system kills the virus).


[Antibacterial agents like triclosan] do basically nothing to the virus!

In sum:

Water is not very effective alone in washing the virus off our hands. Alcohol-based product works better. But nothing beats soap – the virus detaches from the skin and falls apart very readily in soapy water.

The study below found no harms of using bar soap. They inoculated bar soap with 70 times the amount of bacteria you’d find on normal used soap bars and there was no detectable bacteria on respondents’ hands after washing. Bar soap is also better for the environment. Less plastic packaging.

Study: Washing With Contaminated Bar Soap Is Unlikely To Transfer Bacteria, Epidemiology and Infection, 1988

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