Why does soap work?

Why does soap work?

Why does the humble bar of soap work so well on viruses including the COVID-19 virus? Well here are some fascinating facts from Palli Thordarson Professor, School of Chemistry UNSW (University of New South Wales, Australia). I have condensed his tweets below but please have a look at his full thread for all the glorious chemistry detail.

Viruses are very small particles with diameters between 1-100 nm surrounded by a thin polar membrane made of two layers of lipid (fatty) molecule. We know that soap dissolves fat, this is why it’s so good at stain removing too, so when you use soap (bar of soap or liquid soap) to wash your hands, the soap particles dissolve the lipid (fatty) membrane that holds the virus together and this inactivates the virus as it literally falls apart without its lipid membrane. The rinsing of your soapy hands then flushes everything away. So this in a nutshell is why it is so important to wash your hands. 

The advice given is to not just wash your hands - but to wash your hands pretty much after any interaction, going outside, touching a door handle, handling money, going to the supermarket, travelling on public transport, etc etc. 

Wash wash wash your hands. But why so much hand washing? 

The virus can remain active for a relatively long time, even days, and it is particularly long lasting on hard surfaces such as metal or plastic. So if you pick up the virus on your hands from touching a surface (which is highly likely) you need to get rid of it asap, hence the regular handwashing. Did you know that it is estimated that we touch our face every 2-5 minutes? So this means unless you wash your hands regularly you are at risk of infecting yourself from your own hands, transfering the virus to your mouth/nose/eyes by touching your face. You are also at risk of infecting someone else through touch and they will then pass the virus to their face. 

Water is not very effective alone in washing the virus off our hands, because the virus “sticks” to your skin. Alcohol based products work better and these are great to carry when on the move. But nothing beats soap and thorough hand washing action for at least 20 seconds – the virus detaches from the skin and falls apart very readily in soapy water.

With grateful thanks to Palli Thordarson for his clear and understable explanation of the chemistry of how soap works! Check out his Twitter feed (click Twitter link below)

Palli Thordarson


Professor, School of Chemistry UNSW