A towel and wooden hairbrush beside an open doorway, with slippers and a rain-wet lanai overlooking tropical greenery.

Was Grandma Right About Going Outside With Wet Hair?

Dr. Nora Phillips

17 hours ago

3 min read

“Don’t go outside with wet hair. You’ll get sick.”

It’s familiar advice, and it raises a fair question: if cold weather has nothing to do with getting sick, why do we have a cold and flu season?

Grandma’s warning mixed together two different things: feeling cold and catching a virus. Viruses cause colds and influenza, but the conditions around us can affect how easily those viruses spread.

Wet hair does not give you the flu

You need exposure to influenza virus to catch influenza. Wet hair, a passing rain shower, or a chilly room cannot cause that infection on their own. The common cold is also caused by viruses, although they are different from the viruses that cause flu.

Drying your hair may make you more comfortable. If you get sick after being out in the rain, the timing alone does not tell you where or when you caught the virus.

So why does winter matter?

Cold weather changes several things at once. People spend more time together indoors, where poor ventilation can let virus-containing particles build up. Temperature and humidity also affect transmission. Influenza tends to spread more easily in cold, dry conditions, and dry air can affect the mucus that helps clear particles from our airways.

That is different from saying that one cold breeze “weakens your immune system” and gives you the flu. Weather can make it easier for a virus to spread, but the virus still has to be there.

The rabbit hole involves guinea pigs

Researchers have actually tested this. In a 2007 study, they placed infected and uninfected guinea pigs in controlled temperature and humidity conditions. Influenza spread more readily in cold, dry conditions.

It is an interesting piece of the seasonal puzzle, with an important limit: a controlled animal experiment is not a study of people walking outside after a shower. It supports a role for the environment in transmission. It does not prove that wet hair makes people catch flu.

Hawaii does not need winter weather to have flu

Here, we can have a sunny afternoon and plenty of influenza circulating at the same time. The Hawaii Department of Health notes that seasonal flu circulates year-round, with activity generally more common in fall and winter and often increasing in October.

That makes the thermometer outside a poor guide to whether we should be thinking about flu. We still share classrooms, offices, cars, and indoor gatherings even when nobody needs a winter coat.

What is more useful than worrying about wet hair?

Keep up with recommended flu vaccination, improve indoor airflow when practical, and stay home when sick. A well-fitting mask can add protection in crowded indoor settings or around someone at higher risk of serious illness.

For returning to usual activities, both of these should be true for at least 24 hours: your symptoms are improving overall, and you have no fever without taking fever-reducing medicine. Take added precautions for the next five days, because feeling better does not necessarily mean you have stopped spreading the virus. Follow any additional school or workplace requirements.

If flu symptoms develop and you are at higher risk of complications or feel very ill, contact your healthcare provider promptly. Antiviral treatment works best when started within two days, but later treatment can still help some people. Do not assume you have missed your chance to ask.

So I would keep the towel handy and give Grandma credit for wanting everyone warm and comfortable. When it comes to preventing flu, though, I would pay more attention to the air we share than whether someone’s hair is dry.