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Hand cleaning

We are all cleaning our hands more regularly during the COVID-19 pandemic. Why does it make a difference? And what is the best way to clean our hands?

In the 19th century, Hungarian doctor Ignaz Semmelweis discovered that regular handwashing could prevent the spread of infections. Seeing a lot of infections and deaths in pregnant women in one of his hospital wards, he put the worrying trend down to doctors unknowingly carrying ‘cadaverous particles’ from the autopsy room to the next-door maternity ward. The death rate soon fell after he made doctors regularly wash their hands with chlorine.

During the Crimean War a few years later, ‘Lady with the Lamp’ Florence Nightingale realised the importance of handwashing too. Though she mistakenly believed infections were caused by rank odours called miasmas, by making doctors and nurses wash their hands she still reduced infections in her war hospital.

Despite these early examples from over 150 years ago showing that clean hands save lives, it was only in the 1980s that good hand hygiene practices in healthcare became the norm. Fast forward to today and regular handwashing has become a ritual for many of us, seen as a key defence against transmission and infection of SARS-CoV-2, the virus responsible for COVID-19. But how does handwashing protect us?

Touching surfaces

One way coronavirus is thought to spread is by people touching infected surfaces or objects. Like any infection that affects the lungs, droplets riddled with the virus form in an infected person’s airway. These droplets come out from the mouth and nose during breathing, talking, coughing and sneezing. Then, if they’re big enough, the droplets land and stay on surfaces.

Someone who touches one of these surfaces is not infected straight away. What happens is that at some point the person will end up touching their face - on average we touch our face 23 times an hour! This is how the virus sneaks into the body, through protective liquid layers in the eyes, nose or mouth that act as pathways to the throat and lungs.

Unfortunately, sneezing can fire large droplets up to six metres, and coughing or sneezing creates a ‘respiratory jet’ that becomes a turbulent cloud filled with droplets of all different sizes. This cloud can travel and settle even further from the infected person.

Given the virus survives on many types of surfaces for hours or days - with one study finding it remains on spongy surfaces in cool, dark places up to 28 days - the only protection against this way of catching the virus is by regularly disinfecting all surfaces and washing hands.

Hand-washing or sanitising for at least 20 seconds after you've been out in public or touched surfaces in a common area can help prevent infection.

Cleaning hands effectively

But a quick rinse under the tap is not enough. Hand cleaning is only effective if done properly, with soap and water or with alcohol-based hand sanitiser. Surfactants (chemicals that let liquids soak into things better) in soap and alcohol (60% or more) in hand sanitiser are key. When they come into contact with the virus, they effectively dissolve the fat membrane that surrounds and glues it together, making the virus inactive.

Our skin’s rough and wrinkly surface can make it hard to remove every last trace of the active virus. This is why health officials advise that whether you are washing with soap and water or alcohol-based hand sanitiser, you should spend at least 20-30 seconds scrubbing and rubbing. The World Health Organization has resources to show you the best ways to do it.

If you use hand sanitiser and apply these steps, when your hands are dry, your hands are safe. But if you use soap and water, two final steps are necessary. First, rinsing your hands under clean, running water removes any remaining dirt, grease and microbes, and washes away the soap to avoid any skin irritation. Second, drying your hands is a critical final safety measure, as studies have shown that wet hands pick up germs far more easily than dry hands.

Hand sanitiser or soap and water?

Given hand sanitiser dispensers litter hospital corridors throughout the world, you would be forgiven for thinking that it must somehow be better than soap at protecting against germs. You would also be wrong.

Both hand sanitiser and soap and water effectively neutralise SARS-CoV-2. Hand sanitiser’s only advantage is that it is the quickest and easiest way to clean your hands. Soap’s most important advantage over hand sanitiser is that it disrupts the sticky bond between the virus and your skin, allowing the virus to slide off with the water down the plughole. It literally washes away coronavirus.

In addition, and unlike hand sanitiser, soap removes grease and dirt from the skin that could harbour virus droplets. Also, soap never goes off. Technically, neither does hand sanitiser, but it has an expiration date for a reason - alcohol evaporates easily when exposed to air because of its relatively low boiling point. This means over time some alcohol will escape. Manufacturers choose an expiry date that is roughly when the alcohol percentage drops below 90% of the original amount. So, avoid expired hand sanitiser.

Taken together, these advantages point to old-fashioned, cheap and readily available soap and water winning hands-down. The advice is clear: if soap is unavailable or impractical use hand sanitiser, but if you’re given the choice of hand sanitiser or soap and water, head to the sink.