How Simple Soap Kills the Coronavirus

Washing your hands with soap is one of the best things you can do to help stop the spread of coronavirus. A single drop of ordinary soap in water is enough to rupture and kill many types of viruses and bacteria (including COVID-19). Why is it so deadly against them?

Soap is made of pin-shaped molecules, with a hydrophilic (‘water-loving’) head, and a hydrophobic (‘water-shunning’) tail. The hydrophobic tail repels water and prefers to link up with oils and fats. So if you put soap molecules in water, they tend to form little bubbles, called micelles, with the water-loving hydrophilic heads on the outside, and the water-avoiding hydrophobic tails on the inside.

Many viruses and bacteria have lipid (fatty) outer layers. These outer layers are like double-layered micelles, with two rings of hydrophilic heads between two bands of hydrophobic tails. The layer also contains protein spikes that allow viruses to infect cells (or for bacteria, perform various important actions that keep them alive). Some of the viruses with this structure include the coronaviruses, HIV, hepatitis B and C viruses, and herpes viruses. (The bacteria with this lipid outer layer include many of those that attack the intestines, nose, throat and lungs.)

When you wash your hands with soap and water, you surround any micro-organisms on your skin with soap molecules. Remember that the hydrophobic tail of the soap molecule tries to get away from water and to link up with fats, like the lipid outer layer of a virus. So the tails of the soap molecules wedge themselves into the lipid layers of the virus, breaking up the layer. According to Prof. Pall Thordarson (acting head of chemistry at the University of New South Wales), “They act like crowbars and destabilize the whole system.” Crucial proteins then spill from the ruptured membranes, destroying the virus.

Some of the soap molecules also disrupt the chemical bonds that allow viruses to stick to surfaces, lifting them off the skin. Soap micelles also form around particles of dirt and the fragments of viruses and bacteria, suspending them in floating cages. When you rinse your hands, all the micro-organisms that have been damaged, trapped and killed by soap molecules are washed away.

So to help stop the spread of COVID-19, please

• Wash your hands with soap
• Practice physical distancing
• Improve your immune system