“You’ll catch a cold going outside with that wet hair,” said almost every parent ever. It’s such a common line that’s been drilled into everyone’s head. But is there any merit to this assumption? Well, the short answer is a big no. The common cold, flu, and many other seasonal respiratory illnesses are caused by viruses, not your scalp’s temperature. Still, there’s something you should be careful about with wet hair.
What really causes your cold
Neither wet hair nor cold weather in particular will make you sick. We get sick with a cold due to becoming infected with one of the 200 different viruses known to regularly trigger inflammation of membranes that line the nose and throat. This happens when we come in contact with airborne droplets that are coughed or sneezed into the air by someone who is sick or when we touch a contaminated surface, whether it’s through a handshake or touching a doorknob.
But if that’s the case, why is this myth so prevalent? In all likelihood, this is a case of misinterpreting correlation as causation. People also suffer from confirmation bias and will tend to notice the times they get sick but ignore the times they were outside in wet clothes or with wet hair and didn’t get sick.
Viral infections spike during the cold season, with cases ramping up starting in October and peaking at the height of winter, usually in February. But while the cold definitely has something to do with a rise in respiratory infections, it’s probably not for the reasons you might think.
During winter, we spend much more time in enclosed spaces, typically closer to each other, so there is more face-to-face contact. Since the frequency of contact with other potentially infected people increases, so does the risk of infection. Around a quarter of people who have an infection with a common cold virus do not experience any symptoms at all, so there’s no way of telling who might be a viral host unless they get tested.
Another reason why we’re likely to get sick is because of the low humidity that we have in the wintertime. Because the little bit of moisture that surrounds viral particles evaporates, these tiny viruses can stay in the air for a prolonged time, increasing the chance you’ll sniff one in.
At the height of the pandemic, common cold and flu cases dropped by nearly 98% because of stay-at-home orders, mask mandates, and a significant uptick in adherence to strict hygiene rules. Now that people have relaxed a lot, these infections have come back with a vengeance as cases of influenza and respiratory syncytial virus (RSV) — a seasonal virus that usually causes mild cold-like symptoms — are surging in the Northern Hemisphere. This perfectly illustrates that weather or body temperature by themselves cannot make you sick.
There is also some research that suggests that a Vitamin D deficiency owed to poor exposure to sunlight may make people more susceptible to infections due to a weakening of the immune system, although this is rather contentious.
None of these things, however, suggest that wet hair or wet clothes make you more prone to getting a cold. The fact of the matter is that you can only get sick if you are exposed to germs, regardless of the weather or how wet your hair is — at least, there’s no research supporting anything otherwise.
There’s only one situation when wet, cold hair may be associated with illness: when you’re already infected. Viruses that cause the common cold or the flu have an incubation period of 24-72 hours, and a low body temperature may trigger the onset of symptoms quicker than they would normally have appeared. But you would’ve probably still gotten sick regardless, it’s just that the wet hair accelerates this process. Another thing to note is that for people with sinus-related problems sudden changes in air temperature can cause sinus inflammation that can cause a runny nose. This is often mistaken for the flu.
Here’s when you should be careful with hair though
It’s highly unlikely that wet hair causes respiratory infections, but it may be responsible for an entirely different beast. Bacteria and fungi absolutely adore warm and moist environments, which is why we have conditions like diaper rash and athlete’s foot, fostered by the accumulation of sweat in the body’s crevices. If you go out with wet hair in warm weather, like you’d expect in tropical latitudes, for instance, there’s a risk of infection. Not a huge risk, but it’s non-zero.
What’s more problematic is sleeping with wet hair. Your pillow and bedsheets have fungus and bacteria you brought home with you from outside. By standing still and transferring heat from your body to the pillow and bedsheet you may foster bacterial and fungal growth. These infections include aspergillosis (caused by a mold found on pillows), malassezia folliculitis (an itchy, acne-like condition caused by yeast infection), and scalp ringworm (a fungal infection that causes a red, itchy, ring-shaped rash). Sleeping with wet hair may also damage it.
In summary, wet hair isn’t a magnet for viruses and there is no evidence that it enhances the risk of getting sick. Instead, here are six proven tips that can protect you from catching the cold:
Wash your hands often with soap and water.
Disinfect the kitchen and bathroom countertops, especially if someone in the household is sick.
Use tissues when sneezing and coughing.
Don’t share drinks and utensils with others.
Eat a healthy diet and exercise often to prop up the immune system.
And, obviously, try your best to steer clear of sick people.
Tibi is a science journalist and co-founder of ZME Science. He writes mainly about emerging tech, physics, climate, and space. In his spare time, Tibi likes to make weird music on his computer and groom felines.