Why alcohol-based hand sanitiser doesn’t kill norovirus and five other winter illness myths
From wet hair causing colds to sweating out a fever, here’s the science behind six stubborn winter health myths.
- 5 February 2026
- 7 min read
- by Linda Geddes
Each winter, the same advice starts doing the rounds: bundle up or you’ll catch a cold, sweat out a fever, guzzle vitamin supplements, trust the colour of your snot.
Some of these beliefs sound harmless, even logical, but often they aren’t backed by science.
Research comparing alcohol hand rubs with soap and water has found that while sanitisers work well against some viruses, such as influenza and rotavirus, they are much less effective against hardier viruses such as norovirus and adenovirus.
As coughs, fevers and stomach bugs spread, here’s what the evidence says about six of the most persistent winter health beliefs – including why hand sanitiser might not be as protective as you think.
Myth: Alcohol gel kills norovirus
Alcohol-based hand sanitisers kill many germs, but they’re less effective against some tough causes of vomiting and diarrhoea, including norovirus, Cryptosporidium (a parasite that spreads through contaminated water) and Clostridium difficile (a bacterium that can cause serious gut infections). Neither do they remove harmful chemicals like pesticides or heavy metals.
Research comparing alcohol hand rubs with soap and water has found that while sanitisers work well against some viruses, such as influenza and rotavirus, they are much less effective against hardier viruses such as norovirus and adenovirus (which causes common cold-like illnesses).
In fingertip tests, washing with soap and running water removed more of these stubborn germs than alcohol gel alone.
Sanitiser can still be useful – especially when soap and water aren’t available, such as on public transport or outdoors. But many people don’t use enough or rub it in for long enough.
Choose a product with at least 60% alcohol, cover all surfaces of your hands, and rub until dry. For the most reliable protection though, wash thoroughly with soap and water and dry your hands properly.
Myth: Going out with wet hair gives you a cold
Colds are caused by viruses, not by being chilly or damp. You can only get sick if you’re exposed to an infected person or contaminated surfaces.
Laboratory experiments in which volunteers were exposed to common cold viruses and then chilled at different stages found no evidence that being cold increased their chances of developing an infection.
Cold weather may still play an indirect role in winter illness, though. People tend to spend more time indoors in close contact with others when it’s cold, which makes it easier for infections to spread.
Laboratory experiments in which volunteers were exposed to common cold viruses and then chilled at different stages found no evidence that being cold increased their chances of developing an infection.
Some viruses – including rhinovirus, influenza and SARS-CoV-2 – also survive and remain infectious for longer in colder temperatures and at lower levels of humidity.
Cold, dry air can also dry out the mucous membranes in the nose and throat, potentially weakening this first line of defence and making it easier for viruses to take hold.
Myth: You can sweat out a fever
Fevers aren’t toxins that need to be ‘sweated out’.
They’re triggered when immune cells detect signs of an infection and release chemicals that signal the brain to raise the body’s internal thermostat, causing your temperature to rise.
Some scientists think fever may be an evolved defence strategy: certain immune cells appear to move faster and work more effectively at slightly higher temperatures (around 38°C to 40°C).
But very high temperatures can be dangerous, which is why doctors tend to focus on monitoring symptoms and using fever-reducing drugs when someone is very uncomfortable or their temperature climbs too high.
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Wrapping yourself in heavy blankets or overheating a room doesn’t force a fever to break – and may increase dehydration and strain on the body. It’s better to stay comfortably warm, drink plenty of fluids and rest.
If a fever is very high, lasts more than a few days or comes with worrying symptoms like confusion, chest pain or trouble breathing, you should seek medical advice.
Myth: Green snot means you need antibiotics
When you have a cold or other respiratory infection, your immune system sends white blood cells to fight it. In the process, these cells release enzymes that can turn your snot yellow or green.
The longer this mucus sticks around, the more vivid its colour may be. But while it may look unpleasant, green or yellow snot is a normal sign that your immune system is responding to an infection and doesn’t indicate which type of germ is the source.
A common myth is that green mucus means you have a bacterial infection and therefore need antibiotics.
In reality, most upper-respiratory tract infections – including colds and many sinus infections – are caused by viruses, which don’t respond to antibiotics.
Because unnecessary antibiotic use contributes to side effects and antimicrobial resistance, doctors look at the overall pattern of symptoms – such as how long they’ve lasted, their severity and whether they’re getting worse – when deciding if antibiotics might be helpful.
Green mucus is also common in acute bronchitis, another condition that's usually caused by viruses.
In this case, inflammation in the airways can turn sputum – thick mucus coughed up from the lower airways and lungs – yellow or green.
In otherwise healthy people, this colour change doesn’t mean antibiotics will help. However, for people with underlying lung conditions such as chronic obstructive pulmonary disease, green sputum can signal a higher risk of bacterial infection, so medical assessment is important.
Myth: You’re not infectious once your symptoms get better
During the COVID-19 pandemic, many people learned that it’s possible to transmit SARS-CoV-2 before symptoms start and sometimes for days after they begin to improve.
Norovirus symptoms typically appear one to two days after you become infected and last for two to three days, but norovirus is most infectious from the start of symptoms until 48 hours after they have stopped.
Studies also showed that people could shed large amounts of infectious virus irrespective of how severe their symptoms were.
That pattern isn’t unique to COVID-19. Several common winter infections can also spread outside the window of obvious symptoms.
People with flu are most contagious during the first three days of illness, but they can start spreading the virus one or two days before symptoms appear. Most otherwise healthy adults remain infectious for up to a week after becoming sick, but young children and people with weakened immune systems may be contagious for longer.
Norovirus symptoms typically appear one to two days after you become infected and last for two to three days, but norovirus is most infectious from the start of symptoms until 48 hours after they have stopped.
Viral shedding of rhinoviruses – a common cause of the common cold – can begin several days before cold symptoms appear, peaks during the first week of illness (around days two to seven) and may continue for up to three to four weeks.
Myth: Loading up on supplements can protect against colds
Sales of vitamin C, zinc and other “immune-boosting” supplements surge each winter. But for most people eating a reasonably balanced diet, there’s little evidence that high doses prevent respiratory infections like colds and flu.
Vitamin C has been studied for decades. A Cochrane review of 29 trials found that taking it regularly didn't stop people catching colds, though it slightly reduced how long symptoms lasted and how severe they were. Starting vitamin C supplements after symptoms began didn’t seem to help.
A separate Cochrane review found zinc supplements also did little to prevent colds. Taken after symptoms started, zinc might shorten a cold by a couple of days, but study results varied, and the evidence was uncertain.
Vitamin C has been studied for decades. A Cochrane review of 29 trials found that taking it regularly didn't stop people catching colds.
What about vitamin D? A World Health Organization review of the research noted that while low vitamin D levels are linked to a higher risk of respiratory infections, evidence that supplements prevent colds or flu is inconsistent and doesn’t justify universal use for this purpose. In some higher-latitude countries, however, vitamin D is recommended during winter mainly for bone health, not immunity.
Overall, supplements aren’t a shortcut to avoiding winter bugs. The most reliable protection still comes from the basics: vaccination where recommended, good hand hygiene, fresh air and ventilation, adequate sleep and not smoking.
