How Soap Kills Viruses

By Adam Calder 

On March 13, the New York Times ran an article written by Ferris Jabar on not only how effective soap is at cleaning away dirt, but also how the physical properties of soap actually destroys viruses.

Soap achieves these feats by virtue of its chemical structure.  Soap molecules are made of two ends. The head of the molecule bonds readily with water (hydrophilic) and the tail repels water (hydrophobic).  The tail prefers to bond with oils and fats (lipids).

When soap molecules are mixed in with water, some of them float about individually, some interact with molecules of dirt and debris to form small balls called micelles.  When these micelles form, they have their hydrophilic ends facing out and the hydrophobic ends all pointed in to the center of the ball of soap molecules.

Some viruses, including the coronavirus, have lipid membranes that are structured with two hydrophilic heads surrounding two hydrophobic bands.  As you wash your hands properly with soap and water, any microorganisms that happen to be on your hands get enveloped in soap molecules.

The hydrophobic ends of the soap molecules are repelled by the water, and during that process the lipid-loving end of these molecules work their way into the lipid shell of viruses.  The opposing forces of the two ends of the soap molecule actually pry apart the protective shell of the virus.

Once the virus shell is compromised, the whole virus is destabilized.  The genetic information of the virus coded inside proteins within the protective shell begins to spill out into the surrounding water.  This leaves the virus useless at propagating itself, and it soon dies.

Viruses and bacteria have a chemical structure that makes them stick to surfaces.  Soap molecules interfere with that bond and allows these microorganisms to be lifted off the skin.  Micelles form around the bits of dirt, broken virus pieces and whole viruses and enclose them in floating bubbles.  When you rinse your hands after scrubbing with soap and water, all of that flotsam gets washed down the drain.

Alcohol hand sanitizers work similarly to defeat viruses by attacking their lipid membranes, but hand sanitizer is not very good at lifting the viruses off of your skin the way soap does.

Some viruses and bacteria do not rely on a lipid membrane, and instead rely on protein or sugar shells.  Soap isn’t as good at killing these types of microorganisms, but it is good at lifting them off of your skin in a way that alcohol sanitizers cannot.  For these reasons, soap is a more reliable and effective way to remove pathogens from your skin.

With proper use, soap can help keep you, your family and your community safe.  The power to do this rests literally in your hands.  All you need to add is a little soap and water.