Remember snow days when you were a kid, when your mom wouldn’t let you go out and play until you were layered under a veritable mountain of jackets and sweaters? Or that time your grandma told you that you’d “catch your death” by walking to meet your friends in January?

Most of us grew up believing that cold weather was a threat to our health—and, yeah, freezing temperatures are pretty dang dangerous when it comes to issues like hypothermia and frostbite. But when it comes to run-of-the-mill “winter illnesses” like the sniffles, the chill factor isn’t really the problem. In fact, some research indicates that cold environments might actually be good for us, and skipping gloves on a chilly day might lead to chapped hands, but it’s probably not going to give you a virus.

So if cold air isn’t as harmful as we thought, why do we think it is? Why has this belief been passed down for so many years?

Well, for starters, rates of flu and viruses are higher in the winter.

Flu cases in the U.S. usually peak between December and February each year. Viruses, colds, and strep throat are more common during the winter months—but not necessarily for the reason you’d think. Exposure to cold weather itself doesn’t bring on a case of the flu, like your grandma may have believed, but winter climates do play a sneaky role in illness by enabling the flu to spread.

“Studies have shown that certain viruses—like the ones that cause the flu—thrive and spread most effectively in cold, dry weather,” says Chad Masters, M.D., regional medical director of MedExpress Urgent Care. (Whereas heat tends to kill pathogens like bacteria and viruses.) “This can help explain why cold and flu ‘season’ occurs during the wintertime, and why mild winters can sometimes result in a less severe flu season.”

Unfortunately, bundling up doesn’t really combat this phenomenon—you can still catch a cold whether you’re covered head to toe in knitwear or frolicking barefoot in the snow. (But, you know, don’t actually frolic barefoot in the snow—frostbite is still real.)

So viruses hit a high point in the winter, and when you combine that with sinus-drying indoor heating and the abrupt temperature change of walking into warm buildings from the cold outdoors, you’ve got a not-so-fun perfect storm. Cold, dry air has been associated with the flu and pneumonia and can be terrible for people with asthma, in particular, while fluctuating temperatures can also create blood pressure problems.

In reality, all the time you spend indoors in the winter is probably a much bigger culprit.

Spending months on end cooped up inside doesn’t exactly do wonders for our health. Stuffy air and indoor household allergens like dust can be a hassle—and indoor socializing facilitates the spread of germs.

“Consider those winter holiday gatherings,” Masters says. “Friends and family members congregate in one place to celebrate the holidays and exchange gifts, hugs, food—and germs.” Sure, this sounds a little Ebenezer Scrooge, but the truth is that when the windows and doors are closed, we’re all breathing pretty close to one another, both at home and at work. (I know, it sounds kind of gross when you think of it this way.)

On top of this, spending time indoors contributes to seasonal health issues due to lack of vitamin D from the sun. “The theory I think holds the most weight is that we’re depleted of vitamin D by the time January comes around,” suggests food expert Katie Kimball of Kitchen Stewardship. But if you feel like you’re not getting enough vitamin D, your doctor can find out whether you’re deficient with a quick blood test and prescribe supplements to get your levels back up.

It also doesn’t help that everyone is really freaking tired.

Getting a good night’s sleep can be a challenge any time of year, but winter is especially great at throwing a monkey wrench into our sleep schedules. Earlier sunsets, the lack of vitamin D, and winter blues… all of these factors can make it harder to get your zzzs. In addition to making us want to nap at our desks, that lack of sleep can also weaken our immune system—making it easier for us to get sick.

Taking care of yourself in the winter goes a lot further than simply bundling up—here’s how to stay healthy.

Staying warm is great, but you can increase your chances of staying healthy this winter by taking good care of yourself: Fill your body with vitamin D-packed foods, get proper sleep, and take time to exercise, and you’ll get that extra boost during a season when stress levels are high and nasty viruses are lurking around every corner. Of course, that’s easier said than done when the winter blues make you just want to eat an entire cheese plate while hiding under your comforter, but still.

1. Get a flu shot.

Flu shots stir up polarizing feelings, but at the end of the day, they’re key to keeping yourself and your community healthy. If you’re healthy enough to get one, it’s important that you do, because it helps safeguard people who are not able to get the shot and would have a hard time fighting off the virus. “It’s so important to get your flu shot before the cold and flu season starts,” Masters says. “A flu shot not only helps protect you from the flu, but also friends, family, and coworkers too.”

2. Exercise.

Breaking a sweat is good for both your mental and physical health in the colder months. Regular workouts can contribute to a strong immune system and can improve your mood. (And of course, if your winter goals include having an IRL peach emoji butt, exercise can help with that too.)

3. Take care of your mental health.

Many people suffer from Seasonal Affective Disorder (SAD), a type of depression typically brought on in the winter months. Even if you just experience mild winter blues, don’t forget that it’s worth taking a few minutes out of your day to nurture your mental health. This could mean taking some time to do something that makes you happy, like reading a book or taking a walk. It could also mean reaching out to your favorite people, prioritizing getting a healthy amount of sleep, or talking to a therapist. Some people swear by light therapy, which can help increase your mood on gray days.

4. Wash your hands.

Like, a lot. Wash them before and after handling food, whenever you blow your nose or touch garbage, and after you hold onto a grimy pole on public transit. Take care not to touch your face too often during the day to avoid transmitting germs. (I can’t be the only one who uses my hand as a chin rest when I’m sitting in front of my laptop.)

When it comes down to it, spending a day out in the cold isn’t really going to cause a cold. You’ll still want to bundle up, but that’s just because nobody likes to be shivering during their morning commute. (And because hypothermia. Nobody wants hypothermia, right?)

Knowing the true reasons for winter illness is one of your first lines of defense for staying well, so use your newfound wisdom to send colds and flu packing. Here’s to a healthier winter season.

Claire Hannum is an NYC-based writer, editor, and traveler.