Chances are you've heard all of these medical claims hundreds of times, but just because they're an ingrained part of our society doesn't make them true. Learning from these medical myths can save you a lot of time, effort and, in some cases, physical stress.

1) Humans use only 10% of their brains.

Brain scanning technology has shown that for a given activity, humans might use only the portion of the brain that controls that activity, but during the course of the day, pretty much all of the brain is used.

2) Eating turkey makes you sleepy.

Turkey does contain tryptophan, an amino acid that acts as a natural sedative, but 1) it only works on an empty stomach,  2) it's got no more tryptophan than chicken or ground beef, and 3) the amount eaten at a typical Thanksgiving meal isn't enough to have much of an effect. That "turkey coma" you slip into on Thanksgiving has more to do with the heavy, carbohydrate-rich meal than the turkey itself. (The alcohol doesn't hurt either.)

3) You can cure a hangover.

There is no scientific evidence of an effective "cure" for hangovers. Drinking in moderation is the best prevention.

4) You should rhythmically cough during a heart attack to increase your chances of survival.

This bit of advice has made its way around the Internet, forwarded in emails (including the occasional PowerPoint presentation) by people whose good intentions have allowed it to circulate for over a decade. "Cough CPR" is actually a real phenomenon that could theoretically save someone's life during a heart attack, but it is only useful in a specific situation -- when the person is on the verge of losing consciousness and entering cardiac arrest -- and should be attempted only under the instruction of a medical professional. The process requires precise timing and if done incorrectly or done by a person not going into cardiac arrest, it could actually cause harm OR DEATH. This isn't the sort of thing you want to risk trying on your own based on the instructions in an email.

5) Sugar causes hyperactivity in children.

Several studies have failed to find a link between sweets and hyperactivity in kids and have actually found that the perceived boost in activity is in all in parents' minds. They assume that sugar will cause hyperactivity, and so that's what they see happen.

6) It takes seven years for chewing gum to fully digest.

This may be an old wives' tale to prevent kids from swallowing gum. Although the body doesn't break down chewing gum as it does with food, it doesn't remain in the body for seven days, much less seven years. It comes out "in the end" in a timely fashion, along with everything else you eat.

7) Eating late at night will cause you to gain more weight than eating earlier in the day.

This seems to make some sense, given you don't burn off as many calories while you sleep, but numerous studies have shown that it doesn't matter when you eat, just what and how much you eat.

8) The artificial sweetener Aspartame causes cancer, multiple sclerosis and other diseases.

Aspartame, the key ingredient in artificial sweeteners like NutraSweet and Equal, has been the subject of rumors of its disease-causing potential since the '90s, but none of the outrageous claims has yet to be substantiated. Its safety has been verified repeatedly by the US Food and Drug Administration (FDA), which deemed it "one of the most thoroughly tested and studied food additives the agency has ever approved."

9) You should drink at least eight glasses of water a day for good health.

The amount that one needs to drink to replenish fluids lost during the day varies by person, but on average, eight glasses is more than is necessary. Estimates of how much the average person needs daily to balance out lost fluids range from six glasses all the way down to NO GLASSES. That's right; some experts claim that most humans get all the liquid they need to replace the amount they lose through food, not through downing glass after glass of water. That said, drinking additional water can have some health benefits, but don't feel that if you don't drink eight glasses a day you are somehow unhealthy or dehydrated.

10) Swallowing Visine will cause diarrhea.

The Visine-in-the-drink revenge myth has been around for years, but diarrhea isn't among the side effects associated with ingesting Visine's active ingredient, Tetrahydrozoline. It can, on the other hand, cause nausea, vomiting, hypothermia, seizures, difficulty breathing, coma and death, so this "harmless" prank isn't so harmless after all.

11) More heat escapes from your head than from any other part of your body.

We've all heard the "fact" that you should always wear a hat in the cold because 40%, 50%, 60%, even 90% of your body heat is lost through your head, but studies have shown the true amount to be about 10% -- or the same as any other part of your body.

12) Suicides increase during holidays.

It's easy to see how this myth has been so persistent, with the winter holiday season being stressful to many and the shorter days triggering some people's seasonal affective disorder (SAD), but statistics show that incidents of "self-injury" actully go down during the winter holidays -- by as much as 40%. Sure, some people get the holiday blues, but it seems that's even more impact from the holiday cheer.

13) You can get an ulcer from stress and spicy food.

A peptic ulcer is the erosion of the stomach lining. While stress and spicy foods were once thought to be causes, now it's known that the major cause is a bacterium, Helicobacter pylori. Stress and spicy food don't cause ulcers, but they can make existing ones worse.

14) Low-tar cigarettes are healthier than regular cigarettes.

For over 40 years, low-tar, or "light," cigarettes were thought to be more healthy than regular cigarettes, but in 2008, decades-old government-endorsed testing "proving" the benefits of light cigarettes was nullified. A year later, a 2009 study showed that smokers who switched to low-tar cigarettes were actually 50% LESS likely to quit smoking. That year, the Family Smoking Prevention and Tobacco Control Act was passed, requiring FDA approval for any tobacco company to call their cigarettes "light," "mild," "low-tar" or in any way imply that they are somehow more healthy than normal cigarettes.

15) Microwaving food in plastic containers releases cancer-causing agents into the food.

While it's theoretically possible that a substance used to create a plastic container could seep into food while being microwaved, there's no conclusive evidence of any danger posed by this sort of mishap. Plus, the FDA imposes strict guidelines on microwavable plastics to prevent this sort of thing. To be absolutely safe, stick with microwave-safe plastics, and follow the microwaving directions on food packages.