Why the New Coronavirus Does not Like Soap

Global Handwashing Day - 15 October

I: “Anton, wash your hands”

My son: “Done…”

I: “With soap…”

My son: “Done…”

I: “For longer… three seconds are not enough…”

Sounds familiar? I am sure I am not the only mother/father to have this recurring, and rather monotonous, conversation with our dear offspring each time they get home or sit down to eat; the same our parents surely had with us some decades ago.

However, this conversation has become particularly relevant in times of the new coronavirus –a virus that is mainly transmitted through the air but also by touching our face (nose, eyes, mouth) with contaminated hands. And most of us have the (bad) habit of touching our faces very frequently -once every two to three minutes, in average.

To date, we do not have an effective treatment against this virus -several months and millions of euros are still needed to test the efficacy of the first specific treatments. But we do have an incredibly powerful and cheap preventive measure: soap.

To date, we do not have an effective treatment against this virus. But we do have an incredibly powerful and cheap preventive measure: soap

On an earlier occasion I wrote about hand hygiene, a measure that has saved millions of lives and the efficacy of which we do not question today, although it cost a young Austrian physician his position- and his sanity- when he tried to convince his colleagues of this in the 19^th century.

Even if today we all accept the importance of washing our hands, many of us may not be aware of the reason, at the molecular level, why soap works so well against viruses and other microscopic “bugs” that so happily stick to and travel on the surface of our hands.

Viruses and Soap

Soap is obtained by combining animal fat or plant oils with an alkali base (bleach) dissolved in water. The molecules that compose it have a hydrophilic “head” that likes water and a hydrophobic tail that does not like interacting with water but likes lipids. In turn, many bacteria and viruses, including coronaviruses, are surrounded by a protective lipid layer. In fact, it is a double layer in which, much like a sandwich, the hydrophobic tails are pointing inside and the hydrophilic heads are pointing outside.

Now, what happens to the virus when we wash our hands with soapy water? The hydrophobic parts of the soap molecules try to hide from the water, and to do so they insert themselves into the lipid layer that surrounds the virus. This acts a bit like a “crowbar”, prying the membrane apart and breaking up the virus. The soap molecules then surround the fragments of virus, bacteria, dirt or any other particle attached to our skin and form small spheres (or micelles) with the hydrophobic part looking inside and the hydrophilic part looking outside. Add some water to wash all that away, and that’s that.

Now, breaking the lipid layer that covers and protects the virus takes some time, and that is why Anton’s three seconds are not enough. The World Health Organisation (WHO) recommends washing your hands during at least 20 seconds (or, if you like singing, the time it takes to sing Happy Birthday twice). Instead, the type of soap we use is not important -no need to spend more on “antibacterial” soaps- nor is the temperature of the water – no need to boil our hands.

Now, breaking the lipid layer that covers and protects the virus takes some time, and that is why Anton’s three seconds are not enough. The WHO recommends washing your hands during at least 20 seconds (or, if you like singing, the time it takes to sing Happy Birthday twice).

Certainly, in the absence of soap and water¹ we can use hydroalcoholic gels (with an alcohol content equal to or higher than 60%) to inactivate the virus, although it works less well if our hands are greasy or dirty, and is less effective than soap in inactivating other types of microorganisms.

Helping to limit the spread of this and other infectious agents is, literally, in our well-washed hands.

_

¹ 820 million children worldwide lack access to handwashing facilities in their schools, according to a recent UNICEF report.