Sorry, you need to enable JavaScript to visit this website.

How Soap Works: The Science Behind Handwashing

While there’s still much we don’t understand about COVID-19, there's one piece of advice that experts in the health care community agree on: washing your hands with soap and water is one of the most effective ways people can keep from getting sick, and from passing the virus to others1.

Soap, which has been in around for thousands of years,2 is uniquely structured to help destroy the virus. “Soap works because it’s the right structure to do the job,” says Rebecca Gallego, senior principal scientist, medicinal sciences with Pfizer. “No mater how hard you try, if you were to scrub with just water, or if you were to scrub with sand, it wouldn't work.” 

Here’s why it’s soap is so effective:

Coronavirus molecules look a bit like spiky sea urchins. The outer layer is a plasma membrane made of two layers of phospholipids. The phospholipids consist of a greasy lipid part that is hydrophobic, meaning it hates water, and a phosphate head group that is hydrophilic, meaning it loves water. The spikes on a coronavirus are made of protein. They help transmit the illness by penetrating a host cell in a human being and transferring the genetic information of the virus, which then replicates itself. That’s when a person gets sick.

And that’s what soap is able to stop.

A soap molecule, which looks like a tadpole, has a hydrophilic (water-loving) head and a hydrophobic (water-hating) tail. The water-hating part of the soap wants to get away from the water. If the virus is on a person’s hands, that water-hating tail is drawn to that fatty layer. It pries its way in.

“When soap comes into contact with the plasma membrane of the virus, it’ll try to wedge itself in there,” says Gallego. “If you get enough of these soap molecules into the plasma membrane, it breaks it apart, destroying it.” The virus pops like a balloon, spilling its insides.

When a person scrubs his or her hands for 20 seconds, as the CDC guidelines recommend3, the motion builds up more bubbles, which finds their way into the cracks and crevices of the hands. This allows the soap to do its job more thoroughly by destroying more and more of the virus, preventing someone from getting sick, themselves, and from passing the virus on to others.

Gallego says that this approach is simple, but effective, when done correctly.

“Doing all these little things can add up to a big impact factor when it comes to preventing the disease,” she says.

 


1CDC, “Show Me the Science: How to Wash Your Hands” (first sentence)
2ACI, "Soap and Detergents History
3CDC, "When and How to Wash Your Hands"