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Why soap and water are the best weapons

April 23: The last two months have involved a lot of lengthy, halfhearted renditions of the Happy Birthday song, all of which have been unaccompanied by cake. 

You know the drill. After touching a doorknob or grabbing the mail, you come inside and wash your hands with soap for at least 20 seconds, equivalent to two verses of the birthday song. Hand washing has been so widely cited by experts as the best protection against COVID-19 that a recent study found that Google searches for “wash hands” were correlated with the spread of the COVID-19 outbreak in 21 countries. 

Closeup view of a pair of soapy hands being washed in the foreground over a sink with running water in the background

But as you scrub and hum, you’re probably wondering what makes hand washing with soap and water such a powerful weapon against the virus?

The answers are fat and contact time.

SARS-CoV-2, the coronavirus strain that causes the COVID-19 illness, is an enveloped virus. This means that underneath its now-iconic spikes, the viral molecule is encased in a protective fatty membrane. The spikes on the outside allow the molecule to catch on and easily adhere to human tissue and hard surfaces, while the fatty membrane repels water. This makes it very difficult to dislodge the virus particles using water alone.

This is where soap comes to the rescue. Whether in liquid or bar form, soap is made by combining animal or vegetable fat with an alkaline solution and is composed of collections of two-sided molecules called micelles. The tail of the soap micelle is attracted to oil, and its head is attracted to water. When soap comes into contact with enveloped viruses like SARS-CoV-2, the oil-loving tail of the micelle bonds with the virus’s fatty membrane while the head of the micelle drags the virus towards the water. Eventually, this pulling and dragging breaks open the fatty envelope covering the virus particle, so the viral contents can be rinsed away. 

For soap to do its job well, you must give it sufficient contact time to fully encase any viral molecules present and break them down. Start with a generous amount of soap, then spend your first 10 seconds distributing the lather on the front and back of your hands, in between your fingers, and underneath your nails. Spend your next 10 seconds doing all that once more, then rinse those ruptured molecules down the drain. 

After weeks of relentless hand washing, you may feel tempted to cut your scrubbing short at times. But to do so would be to disable one of the most potent weapons we have against not only this virus, but other germs as well. You may not get any cake when you’re finished singing Happy Birthday, but you’re still getting a pretty great gift.

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