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Coronavirus: How hand sanitisers protect against infections

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As coronavirus continues its spread, panic-buying has swept supermarket shelves of hand sanitisers. What’s in these sanitisers and how effective are they in comparison to hand washing? This graphic takes a look.

Hand-washing has been a custom for centuries. But it was only in the mid-1800s that Ignaz Semmelweiss, a Hungarian doctor, established a link between hand-washing and preventing the spread of disease. Semmelweiss identified that doctors washing their hands before baby deliveries drastically reduced the number of women who died after childbirth.

Today, we have a range of options for hand hygiene. Bar soaps, liquid soaps, antimicrobial soaps, and of course the titular hand sanitisers. As coronavirus spreads, the key advice has been to make sure you regularly wash your hands. But will just using hand sanitiser do instead?

To answer that, we need to take a look at what’s in hand sanitisers. Generally, they come in two varieties: alcohol-based and non-alcohol-based.

The alcohol-based sanitisers usually contain ethanol, the same alcohol found in beer and wine. Other alcohols used are isopropanol (commonly known as rubbing alcohol), and, less commonly, propanol. Usually, alcohol-based hand sanitisers contain between 60-95% alcohol.

Manufacturers add other ingredients for various reasons. These include additional agents which are active against viruses or bacteria, such as chlorhexidine or benzalkonium chloride. These ingredients are also key in non-alcohol-based sanitisers. Ingredients such as glycerol stop your hands from drying out. Hydrogen peroxide, added in small amounts, prevents bacterial contamination of the sanitiser.

Alcohols are effective at killing most bacteria and viruses. They affect the structure of proteins, causing them to become misshapen or ‘denatured’. Through this they destroy the outer shells of viruses and bacteria, killing them and preventing infections.

Though they’re effective in most cases, there are some types of viruses they can’t destroy. These are viruses which don’t have the outer layer (known as an envelope). Coronavirus is an enveloped virus, so alcohols are effective against it. Non-enveloped viruses, such as norovirus, aren’t killed by alcohols.

Chlorhexidine, sometimes added to alcohol-containing sanitisers, is effective against bacteria and viruses. There’s some evidence that its addition to alcohol-based sanitisers increases their effectiveness.

Benzalkonium chloride is often used in non-alcohol-based hand sanitisers. It has some effectivity against bacteria and limited activity against viruses. It’s also slow to act, meaning that non-alcohol-based sanitisers are generally less effective than alcohol-based ones. The CDC states that the available evidence is that benzalkonium chloride is not as effective against coronavirus as alcohols.

So, alcohol-based hand sanitisers work — but are they effective? And how do they compare to just washing your hands?

There are a few criteria that hand sanitisers need to meet to be most effective. Alcohol-based sanitisers are more effective than their non-alcohol-based counterparts. However, the alcohol percentage by volume needs to be at least 60%. Below this, they’re less likely to kill the bacteria and viruses on your hands.

The potency of alcohol-based hand sanitisers increases with the percentage by volume of alcohol. So higher percentages are likely to be better. However, very high concentrations (above 95%) are less effective. This is because proteins aren’t denatured as easily when there isn’t water around.

Another key factor is the volume of hand sanitiser used. It needs to be enough to cover all areas of both hands — otherwise, you’re leaving areas where viruses and bacteria could continue to linger. To properly coat your hands, you need to use about 3 millilitres of sanitiser (approximately a palmful).

Finally, the dirtiness of your hands is also a factor. If they’re covered in dirt or grease, hand sanitiser won’t be effective in removing this. Bacteria or viruses in the dirt on your hands could still remain as a result.

With these caveats, it’s easy to see why recommendations have focused on hand-washing. If you wash your hands for the 20-second period recommended, it’ll remove dirt, grease, viruses and bacteria.

When it comes to the type of soap, any type will do. It doesn’t need to be a special antimicrobial soap to be effective — in fact, studies have shown that these soaps are no more effective than plain soap.

Of course, you won’t always be in a position to be able to wash your hands. In these cases, hand sanitisers certainly have a place and can help ward off bacteria and viruses. However, when it comes down to a comparison between the two, hand-washing is more effective. So you can stop worrying about not being able to buy hand sanitiser anywhere right now!

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