Everyone knows that apples don’t really keep the doctor away. However, that doesn’t stop people from believing plenty of other old wives’ tales. What began as well-known myths have somehow been mistaken for medical facts. What’s more: these falsehoods are so pervasive that most of the population has no idea they aren’t remotely true!

The next time you hear someone rattle off one of these medical myths, you might want to educate them on the truth. Sure, a few might be based on real occurrences or anecdotal evidence, but for the most part, there’s a logical (and scientifically proven) explanation for everything…

1. Going outside with wet hair will make you sick: There is only one thing that makes us sick, and it isn’t our wet hair—it’s germs. So if you’re in a rush, go ahead and leave the house without dealing with your hair dryer! To keep germs at bay, just make sure you wash your hands.

2. Cold weather in general makes you sick: Nope! Remember, only germs can make you sick. In fact, some doctors believe that you’ll recover more quickly if your body is exposed to colder conditions. A drop in temperature has nothing to do with actually getting a so-called “cold.”

3. Supplements make you healthier: While it seems like taking vitamins can do a body good, you should do your homework before you add a supplement to your routine. Studies have shown that older women who take calcium actually have a higher risk of dementia.

4. We only use 10 percent of our brains: This common idea has been spouted by self-help gurus for years as a way to get people to access some sort of hidden potential. If you don’t believe it’s a myth, ask your doctor to perform a scan of your brain activity. There are zero dormant areas!

5. Sugar turns kids into monsters: Studies have long debunked this myth. Kids most often consume sweets during celebrations—like birthday parties—when the rules are lax and they feel free to be rambunctious. It’s not the sugar, but the party!

6. You have to stay awake when you get a concussion or else you’ll die: If you believe that you or someone you know has a concussion, seek medical treatment immediately. However, your doctor will most likely tell you to get lots of rest—not to avoid sleep.

7. Gum stays in your stomach for seven years: Several of the ingredients in chewing gum, like wax, aren’t digestible. But the human body knows how to deal with indigestible food products—we poop ’em out! So swallow all the gum you want if that’s what you’re into.

8. Sitting too close to the TV ruins your eyesight: People say this about holding a book too closely to your face, too; neither are correct. While doing this might make your eyes work overtime and feel sore, there is no evidence that this causes long-term damage to your eyes.

9. You must drink eight glasses of water a day: In 1945, the Food and Nutrition Board recommended that adults drink the equivalent of eight glasses of water a day. However, they also said that most of that water we require is actually already present in the food we eat.

10. Don’t swim for an hour after you eat: There is no evidence that doing any sort of exercise after eating is actually dangerous. Sure, you might feel uncomfortable and get a cramp, but it’s most likely because you just ate too much.

11. Hair and fingernails keep growing after death: The reason people believed this for so long was actually a simple misunderstanding. While your hair and nails might appear longer after you die, that’s just because the body’s soft tissue is retracting as it dries out.

12. Shaved hair grows back darker and rougher: Plenty of people insist they’ve experienced this firsthand, but they’re actually just feeling the blunt edge of the shaved hair growing in. That blunt edge gives it a thick and dark appearance.

13. Turkey makes you super sleepy: Yes, turkey does contain tryptophan, a chemical that causes sleepiness. But in order to feel it, you’d need to eat the entire turkey! So why do people get sleepy after a Thanksgiving feast? Because they’ve eaten too much, duh!

14. Ulcers are caused by spicy foods and stress: For years, doctors thought that your lifestyle or the foods that you ate gave you ulcers. Now they know the truth: ulcers are actually just caused by a bacteria. So, eat all the pizza you want and wait until the last minute to complete that huge assignment—diet and stress won’t cause ulcers in the least!

15. You can’t get pregnant during your period: While it’s highly unlikely that a woman will conceive while she has her period, don’t forget that sperm can live inside a woman’s body for up to a week! And if she happens to ovulate during that week, conception is possible.

16. You lose most of your body heat through your head: There’s some belief that it was hat salesmen who started this rumor. To put it to bed, scientists conducted research and found that only seven to 10 percent of your body heat is lost via your head. Take that, hat hair!

17. Vaccines can make you sick: Vaccines are designed to prevent illness. While the vaccine carries a deactivated dose of the illness it’s treating, you aren’t going to get sick from it (though you might initially feel a small fever). Vaccines not only protect yourself, but the community at large.

18. Suicides increase over the holidays: This sad statistic is, thankfully, totally wrong. In fact, the Centers for Disease Prevention and Control conducted a study and learned that the rate of death by suicide dramatically decreased in the months of December and January.

19. Poinsettias are toxic: Every Christmas, people want to put these plants in their homes—but many don’t because they have such a dangerous reputation. Did you know there’s never been one confirmed death by poinsettia poisoning? That said, eating the plants will make you sick.

20. Chicken noodle soup cures everything: Despite Mom’s insistence, chicken noodle soup is just… soup. That said, it’s exceptionally comforting to eat! Some studies have even indicated that people who eat soup when sick recover faster due to the placebo effect. Go figure!

It’s crazy how these are confused with real science! It never fails to amaze just how many “medical facts” out there are actually medical myths.

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