The Science of Handwashing

While handwashing has always been an effective way to practice good hygiene, due to the spread of COVID-19, its importance is now a national issue. With supplies of hand sanitizer, disinfectant and other cleaning supplies at record lows due to high demand, parents might be able to sleep a little easier knowing that according to the Centers for Disease Control (CDC) the humble combination of soap and water is even more effective at eliminating germs compared to alcohol-based sanitizers.

What is soap anyway?

Soap is a combination of oil or fat, salt, water and an alkali. The earliest known recipe comes from a Babylonian clay container dated to 2800 B.C. According to the inscription, the product was made of fat mixed with wood ash and water. The Babylonians used their soap to wash cotton and wool in preparation for weaving and textile work, and it would take over 1,000 years for a civilization (the ancient Egyptians) to use soap for human hygiene.

Modern-day soap is remarkably similar to its ancient counterparts. Due to its chemical composition, soap molecules have a dual nature: one side is attracted to water and repelled by proteins and fats, while the other side is attracted to proteins and fats and repelled by water.

Why is soap effective?

Soap’s dual nature (which chemists call “amphiphilic”) makes it ideal for destroying viruses. Because one side of the molecule is attracted to fat, it submerges itself into the virus’ fat and protein shell. When water is added to soap, a reaction occurs that causes the virus to break apart. What remains of the virus is then harmlessly flushed down the drain.

The catch is that this reaction is not an instant one. It’s for this reason that the CDC recommends at least 20 seconds of handwashing to ensure maximum effect. For young children, it can be beneficial to help them follow these five steps:
 

1. Wet both hands with clean, hot or cold water and apply soap.
    
2. Lather hands by rubbing them together with the soap. Make sure the soap is applied to the entirety of each hand.
    
3. Scrub hands for at least 20 seconds. This is about the time it takes to sing “Happy Birthday” two times through.
    
4. Rinse hands with running water.
    
5. Dry hands by using a towel or air-drying them.

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