Sidebar: The Science Behind Soap

We’ve been hearing it everywhere these days: wash your hands for 20 seconds with SOAP. Handwashing, as I’m pretty sure many of us know, is one of our most effective ways of making our hands clean of visible dirt. It also removes pathogenic microbes we cannot even see. While we mainly were taught about the joy of washing our hands when we were kids, many of us don’t really realise the true powers it carries. Now healthcare professionals, newscasters, and our friends and family are telling us to wash our hands with soap. 

But why? Why is everyone constantly telling us to wash our hands? How does handwashing even work? How does it help us prevent the spread of SARS-CoV-2?

Sit tight my friends, I’m going to take you on the wonderful journey of the science behind soap and handwashing. 

To begin the journey, we need to understand what soap even is. Chemically speaking, soap is simply a long carbon atom chain with a salt of a fatty acid 1. When we break that down, essentially soap is made up of 2 important chemical parts, a fat and a base. The magic of soap is in its combination of a fat (like animal or vegetable oil) and a base like sodium hydroxide (NaOH) and that recipe has not changed for centuries. 

Fascinating, yet in order to make sure we actually make soap when we combine the fat with a base we also have to include some water and ensure we use the correct concentration and amount of each ingredient. If we do all of this right, the chemical process known as saponification takes place 2

Saponification is a chemical reaction in which the hydroxide (the OH) from the base reacts with the fatty acid from the fat and breaks a special type of chemical bond known as an ester bond. This reaction then allows for soap to be made (see Figure 1 for a quick visualisation of the chemistry.) 

Figure 1. To make soap, a long fat chain (like the triglycerides found in oil) will react with the sodium hydroxide salt. This reaction known as saponification (is a special type of hydrolysis reaction that also involves water which isn’t included in the figure). This reaction results in soap that has a hydrophobic and hydrophilic region and a byproduct, glycerol. 

Another wonderful property about soap is that one side of it is water loving (hydrophilic) and another side of it is water hating (hydrophobic). As we discussed before, a hydrophilic molecule will interact with water molecules no problem, but a hydrophobic molecule cannot. Hydrophobic molecules don’t like to interact with water or anything water-based and would rather interact with fats and fat-like molecules. This is an important feature that we’re going to discuss in a sec, but as a way to spend some time, and practice social distancing, I also suggest watching Fight Club, for reasons I cannot say, they make soap in the movie (if you already saw Fight Club, watch it again after reading this!).

So now we know that soap is essentially made up of a fatty acid chain with a basic salt of sorts, but how does that even clean our hands? Does soap even kill bacteria, viruses, and fungi? 

Well, first of all, soap DOES NOT kill pathogens, it actually helps remove them from our hands. This is crucial as the microscopic pathogens stick to the oil our skin produces throughout the day. So then when we use soap to wash our hands for 20 seconds following the World Health Organisation’s recommendation for handwashing steps, the water hating (and fat loving) component binds to the oils our skin produces (which has the pathogen stuck to it). That’s great so now the oils on our skin forms a bond with the soap we just lathered up, but how does that soap go away? 

Well, remember soap also contains a water-loving component and so when we wash our soapy hands, the water binds with the hydrophilic component and strips it away from our skin! 

This whole process leaves you with squeaky clean hands that can now be used to scratch that itch on your face. 

Now let’s talk a little about why we’re being told to constantly wash our hands during the SARS-CoV-2 Pandemic. During the MERS-CoV outbreak in 2012, studies have shown that proper handwashing protocol with soap and water can significantly reduce the transmission of MERS-CoV and other pathogenic viruses, like Influenza 3,4. This can also apply to our current situation now and can help us limit the transmission of SARS-CoV-2 droplets that may be on our hands and have nowhere to go (if we don’t touch anything that is!). Once we wash those hands, we strip away the oils that the droplets are attached to and hence reduce the risk of infecting ourselves and others. 

Another fascinating property about SARS-CoV-2 and other coronaviruses is that they are an enveloped virus, this means that there is a layer of lipids that encapsulates the virus. So because soap is amphipathic (one side is hydrophilic and one side is hydrophobic), the hydrophobic part of soap that likes to bind fat will bind to the lipid envelope of this virus. This binding to the lipid envelope causes the SARS-CoV-2 virus envelope to break apart which makes it pretty much impossible for actually infect our cells5.

A wonderful journey it sure has been, we know we have to wash our hands and now we actually understand the science behind why! Though I do want to end with a little PSA: sit tight my friends, as hard as it is now, don’t lose hope in all of the scientists and front-line workers who are fighting for you and the world. One of the best ways you can help us help you, is to continue practicing proper handwashing and social distancing 🙂   

1. IUPAC – soap (S05721). doi:

2. Saponification – an overview | ScienceDirect Topics.

3. WHO | Clean Care is Safer Care: Publication and resources. WHO

4. Alshammari, M., Reynolds, K. A., Verhougstraete, M. & O’Rourke, M. K. Comparison of Perceived and Observed Hand Hygiene Compliance in Healthcare Workers in MERS-CoV Endemic Regions. Healthcare 6, (2018).

5. ServiceMar. 12, R. F., 2020 & Pm, 1:30. Does disinfecting surfaces really prevent the spread of coronavirus? Science | AAAS (2020).

Leave a Reply