The science behind hand sanitizer and soap

Hand washing is the single most consequential public health intervention of the last 200 years. For controlling infectious diseases, it’s just about the closest thing to a magic wand that we have, and sanitizers are a close second. Lather and rinse, or rub and let dry, and viruses and dangerous bacteria both are completely neutralized.

But what exactly is the difference between hand soap and sanitizer? Which is more effective and how do they work?

According to an excellent video from TedEd, viruses like SARS-CoV2, the virus that causes COVID-19, are just a bundle of genetic material wrapped in a thin layer of fat. That outer membrane is held together by the presence of water. That’s why the virus thrives in moist environments like the back of your throat and lungs. When the virus gets into the body it clings onto your cells and the genetic material (or RNA) passes through these membranes, triggering the body’s immune response. That’s when you get sick.

Soap is made of similar fat molecules. When these particles come into contact with the virus, it breaks the lipid membrane. The virus disintegrates and is washed away.

Hand sanitizers, on the other hand, work a little differently. They destabilize the virus’ structure by removing the moisture that keeps the membrane intact.

If soap functions as a crowbar prying open the virus ’outer layer, the active ingredient in sanitizer—ethanol, in the the case of Ethisan—would be “like removing all the nails and mortar from a house and then hitting it with an earthquake,” Alex Rosenthal explains in the video for TedEd.

All of this happens in an instant. The reason public health experts recommend washing your hands for 20 seconds or waiting for sanitizer to dry is to ensure full coverage. Your hands are full of microscopic nooks and crannies that the soap or sanitizer needs to penetrate.

The one advantage of soap is that it removes dirt particles which may harbour viruses or bacteria, so if your hands are visibly soiled, hand sanitizer won’t necessarily be able to neutralize the germs hiding in the dirt.

But in all other circumstances, sanitizer is a safe, easy and effective way to keep your hands clean.