The science behind hand sanitizers

Top of the list for keeping yourself safe from the coronavirus outbreak is washing your hands thoroughly with water and soap. If soap and water are not available, then use a hand sanitizer.

But here’s the catch. Not all hand sanitizers will do the job. According to the US Centers for Disease Control and Prevention (CDC), numerous studies have found that sanitizers with an alcohol concentration of 60–95% are more effective in killing germs. The ingredient you need to look out for on the label of your hand sanitizer bottle is ethyl alcohol, also known as ethanol. Anything above 60% concentration is good.

It is quite possible that hand sanitizers with a lower percentage of alcohol might not work well for different types of germs. They may reduce the growth of germs but not kill them.

A 2004 study published in the Clinical Microbiology Reviews journal says the best antimicrobial efficacy can be achieved with ethanol (60-85%), isopropanol (60- 80%) and n-propanol (60-80%). Alcohol attacks viruses and other disease-causing pathogens by damaging their cell structures. Some alcohols damage the layers that envelop the virus, while some just break down the cells. The novel coronavirus, for instance, is an enveloped virus surrounded by a fat layer. Lipid membrane viruses—like the coronavirus—can be killed using alcohol-based disinfectants and hand sanitizers. They simply break down the membrane or the layer of fat, leaving the virus unable to infect an individual. Soap, in this case, is also an effective solution.

According to the CDC, it’s important to remember that hand sanitizers might not be as effective if your hands are greasy or visibly dirty. While hand sanitizers are effective in clinical settings like hospitals, where hands come in touch with germs but are not heavily soiled, they are not really the best option if you have just handled food, played sports or worked in the garden, for instance.

Neha Gupta, a consultant on infectious diseases at the Fortis Memorial Research Institute, Gurugram, says the benefits of alcohol-based disinfectants and hand sanitizers have been known for a long time. “This goes beyond Covid-19, but you should be using hand sanitizers when you have touched any common surfaces, like tables or door handles," says Gupta.

“I think it is more important to remember the six steps for effective hand hygiene: This applies both in the case of hand sanitizers and washing your hands with soap. You need to repeat these steps for a good 20-30 seconds," she adds.

According to WHO, these steps include: rubbing your hands from palm to palm, moving your right palm over the left dorsum with interlocked fingers, palm to palm with your fingers interlocked, back of the fingers to your opposing palms with fingers interlocked, rotational rubbing of the left thumb clasped in your right palm and rotational rubbing—backwards and forwards—with clasped fingers of your right hand on your left palm.