As the public and governments grapple with understanding Covid-19 and how to curb its spread, sales of hand sanitizer gel have soared. In the UK, some supermarkets have already run out and Boots is rationing purchases to two bottles a customer. But is hand gel really effective against coronavirus? And, if so, should we be making our own if it is not available in the shops or online?

Hand sanitizer is not new. In 1966, Lupe Hernandez, a student nurse from Bakersfield, California, patented the idea of an alcohol-based gel to clean hands in the absence of handwashing facilities. However, it was not until the H1N1 swine flu pandemic in 2009 that the product went from being used in institutions to something the public carried with them. That year, sales of antibacterial gels and wipes in the US soared by more than 70% in six months. By 2010, little bottles of the stuff were everywhere – from checkout counters in airport bookshops to online retailers offering customisable dispensers.

The popularity of hand gels has not just been driven by the fear of pandemics. Lucrative opportunities to market them have pushed sales: they now come in pretty, child-friendly colours (bubblegum pink, bright blue) and with wellness-friendly scents (cinnamon, lavender) that are a far cry from the pungent-smelling version found in hospitals.

Sanitizers have also evolved to include other active ingredients in place of alcohol, and there are recipes online for making your own. Good Housekeeping suggests vodka. Wellness bloggers plump for things such as witch-hazel and aloe vera. But are these effective in killing germs?

Hygiene experts, the NHS and Public Health England all agree that to kill most viruses, a hand sanitizer requires at least 60% alcohol content (most contain 60-95%). For those with sensitive skin, there are now options that don’t contain alcohol. For decades, there were also versions made with another powerful antibacterial agent, triclosan, which was found in everything from soaps to toothpaste. However, research has since found that triclosan can be detrimental to the body’s endocrine system, and the US Food and Drug Administration banned its use in hygiene products at the end of 2017.

Sally Bloomfield, a professor at the London School of Hygiene and Tropical Medicine, says that viruses are much more resistant to disinfectants than bacteria. Luckily, she says, coronavirus is an envelope virus, meaning it has a coating around it which the alcohol can attack, thereby eliminating the threat. (Norovirus and rhinovirus, by contrast, do not).

This means that making your own sanitizer, while potentially effective against some bacteria, is not something Bloomfield would recommend. “It’s very unwise, dangerous, even,” she says. Shop-bought products also contain emollients to make them softer on the skin, without which you run the risk of hurting your hands. Getting the mix right at home would very tricky – so it is a big no-no.

The key thing is when to use hand sanitizer. Covid-19 is a new illness, so no one knows exactly how it spreads. According to the NHS, it is likely that it is through cough droplets spread from person to person and very unlikely that it is transmitted through objects, be that packages or food.

Bloomfield’s advice is to wash your hands with soap and water – or, if that is not possible, use hand gel – when you return to your “safe place”, by which she means your home, your desk or work station, or your seat on the train or plane, for example. Avoid touching anything you don’t need to touch, and be mindful of what you do touch – such as door handles and bus poles – and if you can’t wash your hands or use gel after coming into contact with things, do not touch your face.

A virus needs a host – living cells – to reproduce: so don’t rub your eyes, or touch your mouth or any wounds if your hands are not clean. Keep your hands clear until you have access to gel or can wash them.

The best option is soap and water. According to a 2019 study by the American Society for Microbiology, using running water and soap to wash your hands is more effective than a dab of gel that you have not quite rubbed in.

When it comes to hygiene and safety, what matters isn’t a single viral cell, it’s how much of the virus is on any given surface. We don’t have conclusive proof of the extent to which soap can deactivate enough of the viral cells to make a surface safe. However, we do know that washing with soap will dislodge viral cells from your hands, and rinsing thoroughly with water will remove them completely and flush them down the drain. You can touch your hands to your face and not get infected.

So, wet your hands with water, lather them up properly, on both sides, in between the fingers and under the nails, one hand and then the other. Rinse them thoroughly under running water for 20 seconds (or as the NHS puts it, the time it takes to sing Happy Birthday twice). Rinsing thoroughly is key to washing away any viruses. Dry your hands well with a disposable towel, then use that towel to turn off the tap before throwing it away.

It might seem counterintuitive, but a study published in the medical journal Mayo Clinic Proceedings in 2012 concluded that, from a hygiene standpoint: “Paper towels are superior to air dryers.” This is because the towels dry your hands more quickly and more thoroughly than dryers do, and contamination happens more through wet hands than dry.

Lisa Ackerley, a chartered environmental health practitioner, says that stocks of hand sanitizer running low is a problem, but cautions against panic-buying. First, you don’t need to use very much – a little bottle will go a long way. In fact, a spokesman for the chemical products company Kao Corporation reportedly said last week that too much hand gel can cause irritation and skin sensitivity, by drying out the skin and removing natural oils. Damaged skin increases vulnerability to infection, so hand sanitizers, like most things, are best used in moderation – and only when handwashing is not an option.

As Bloomfield puts it, it is not about being paranoid. She likens the process to vaccinations or wearing seatbelts: it is about being disciplined. While some companies have reportedly banned handshaking and other physical contact in an effort to avoid Covid-19, that is not official guidance.

It is impossible not to engage with the world, so you just need to be cautious and methodical in your hand hygiene. “If everyone complies with good hygiene,” says Bloomfield, “then you’re making sure as far as possible that you’re not picking it up, and in the unlikely event you are infected you’re not spreading it.”

• This article was last amended on 6 April 2020. The sentence “Soap has mild antibacterial properties, but it does not kill viruses” was removed and this section of the article expanded to better explain how soap and water is effective against viruses. Also, an earlier version said the NHS compares the advised 20 seconds to wash your hands to being the time it takes to sing Happy Birthday. In fact the NHS says this is the amount of time it takes to sing Happy Birthday twice. This has been corrected.