Handwashing with soap, together with other public health interventions, will be key to curbing the transmission of COVID-19. To understand why handwashing is so effective in killing and removing SARS-CoV-2 it is necessary to understand how soap works at a microscopic level. 

In the image below the green dot represents some dirt or oil that may be on your hand. Pathogens typically reside in the natural oils and moisture on your hand. In the image below, the soap molecule is depicted in red and blue. One side of the soap molecule (the blue part) is hydrophobic, this means that it does not like water, so when you lather soap on your hands this side of the molecule attaches to the oil and dirt. The other side of the soap molecule (the red part) is hydrophilic, meaning that it loves water, so as you apply water to your soapy hands this side of the molecule attaches to the water. As the water washes the soap bubbles away it effectively picks up all the dirt, oil and pathogens from your hands and washes them away. This is why soap is such an effective defence against all pathogens. It is important to remind people that they need to rub hands thoroughly and create a lot of lather so the soap can get into all the cracks and crevices in skin where the virus likes to hide.
    

However, soap not only removes SARS-CoV-2 it also deactivates it. This is because SARS-CoV-2 is an encapsulated virus meaning that its outer layer is made up of a fatty membrane. So when the hydrophobic end of the molecule comes in contact with this fatty membrane it causes it to dissolve and fall apart, thus destroying the virus. For more on how soap works read this article. The image below shows how soap removes and kills SARS-CoV-2.

Source: Dr Harsh Vardhan

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Editor's note

Author: Sian White
Review: Katie Greenland, Ammar Fawzi
Last update: 13.04.2020

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