Regular hand washing - while always important - has been a constant mantra for most of us these past few months. Just the other day a friend asked me if I sing ‘Happy Birthday’ in my head twice to achieve the approximately 20 seconds required to break down germs and viruses. My song of choice is actually Prince’s Raspberry Beret – the chorus from ‘She wore a Raspberry Beret’ to ‘I think I love her’ will get you the required 20 seconds.

But why 20 seconds? Why soap when alcohol-based hand sanitizers are ubiquitous? Let me break down the science.

How does soap work?

The science of hand washing with soap and water is NOT to kill viruses and bacteria, but to attract them and keep them suspended in the soap so that they are removed from your hands through friction along with dirt and washed down the drain. With proper hand washing techniques, soap will remove some viruses from your hands by breaking through the lipid (fatty) layer that encases and protects the genetic material of viruses including Covid-19 and other influenza-causing viruses.

Soap molecules are pin-shaped - one end attracts oil, the other water. 

Why 20 seconds?

The oil-loving end of the molecule attracts the fatty layer of the virus, binds to it, and breaks it apart. This takes a little bit of time - about 20 seconds. There are many studies that dive deep into hand washing, but only two* defined a time period that lowered bacterial levels on your hands – one was a 2012 study presented to the International Association for Food Protection which showed 20 seconds of hand washing reduces the bacteria significantly more than only five seconds of hand washing. Similarly, in 2008 a study published in Applied and Environmental Microbiology found that times approaching 30 seconds were more effective than 15 seconds. This has led to the Centers for Disease Control and Prevention's (CDC) main recommendation of hand washing with lathered soap and water for 20 seconds to bind to that lipid layer and break it apart.

Once your hands are rinsed with water, the broken viruses are washed down the drain along with the soap lather. 

Does hand sanitizer work just as well?

Alcohol-based hand sanitizers work in a similar way - the alcohol works to dissolve the fatty layer of viruses, breaking them apart. While soap and water is always preferable since viruses and germs are physically removed from your hands and washed down the drain, in the absence of water, alcohol-based sanitizer on your hands for about 15 seconds will neutralize viruses.

What is soap, exactly?

Soap is made by mixing fats (an acid) and sodium hydroxide (lye). The resulting chemical reaction produces soap and glycerine. When the fats and oils come into contact with the lye they saponify, or turn into soap. The two most critical components of the chemical reaction are mixing between the acid and the alkali and heat. Once the soap begins to harden, glycerine is created as a by-product of the reaction.

Early soap was made by mixing fat – often tallow or lard – with a caustic (high pH) liquid made by filtering water through hard wood ash.

Prior to World War II, soaps were almost exclusively made using plant or animal based fats. In wartime, the fats and oils traditionally used for soap making were diverted to making explosives, and so new ingredients were needed to make cleaners and bars. At the time, petroleum oil was everywhere, and inexpensive, so petroleum derivatives were used to replace the natural oils and fats previously used to make soap. Because petroleum chemicals were incredibly inexpensive, soap making companies continued to use these ingredients long after the demand for explosives ended.

Studies referenced:

Jensen, D. (2012) Efficacy of handwashing duration and drying methods. International Association for Food Protection, https://iafp.confex.com/iafp/2012/webprogram/Paper2281.html.

Fuls, J.L. (2008) Alternative hand contamination technique to compare the activities of antimicrobial and nonantimicrobial soaps under different test conditions. Applied and Environmental Microbiology, https://pubmed.ncbi.nlm.nih.gov/18441107-alternative-hand-contamination-technique-to-compare-the-activities-of-antimicrobial-and-nonantimicrobial-soaps-under-different-test-conditions/.

April MacKinnon is the owner of Anointment Natural Skin Care, a company dedicated to formulating and manufacturing products that support women physically in their life transitions including postpartum and perimenopause with the intention that physical support will create space for emotional wellbeing. She is the host of Ripple Effect (podcast.anointment.ca), a podcast that explores overcoming self-limiting beliefs, and the mother of three children. She lives in Sackville, New Brunswick with her family, and is an avid runner and yogi.