A chemistry professor explains: why soap is so good at killing COVID-19

One of the most consistent COVID-19 messages from health officials has been the importance of good personal hygiene.

Washing your hands with soap is one of the simplest and most effective ways of killing off any viruses you may have come into contact with.

But why is one of the most everyday, mundane of household items so effective in the fight against COVID-19?

Palli Thordarson is a professor at the School of Chemistry at the University of New South Wales, Australia. He took to Twitter to explain some of the molecular chemistry that helps answer that question.

You can also find up-to-date information on all aspects of COVID-19 on the World Economic Forum’s COVID Action Platform.

Thordarson explains that viruses tend to be made up of three things:

The connections between these three component parts provide the structure of the virus, but those connections are weak – there are no covalent bonds in action that would provide a more stable structure.

Instead, says Thordarson, the viral self-assembly is based on weak “non-covalent” interactions between the proteins, RNA and lipids. Together these act together like a Velcro so it is very hard to break up the self-assembled viral particle.

But it’s possible to break up the particle with soap, which is particularly good at dissolving the lipid layer that surrounds the virus. It also undoes all those other weak bonds within the virus. Once that happens, the virus effectively falls apart.

Washing with water alone is far less likely to shift the virus from the skin surface.

Soap contains fat-like compounds called amphiphiles, which are similar to the lipids found in the virus membrane.

When soap comes into contact with these fatty substances, it binds with them and causes them to disconnect from the virus. It also forces the virus to disengage from the skin.

You do have to be vigorous with your hand-washing though. That’s why the advice is that hands should be washed thoroughly for at least 20 seconds.

No matter how smooth and soft your skin might feel, when you are nanoparticle-sized – like a virus – it is bumpy, uneven, and full of little ridges.

Viruses stick to the skin and get lodged in those minuscule crinkles, which is why shifting them requires active hand-washing.

Other substances are also effective, such as alcohol-based gels. Those with high alcohol content (usually 60% to 80%) will also dissolve the virus. But the antibacterial properties of such products will have no effect on viruses.