14 Common Myths About the Body, Unraveled

Not all body myths are harmful, but facts often become distorted over time.
© MSN Healthy Living // © MSN Health

If you believed everything you heard, you'd never read in the dark for fear of going blind, you’d avoid crossing your eyes to prevent them from staying that way (read about other eye health myths), and you’d eschew dental checkups believing plaque removal loosens teeth (other common dental myths). Not all body myths are harmful, but facts often become distorted over time. Myth-busting experts help separate fact from fiction among these popular, long-standing beliefs.

By Linda Melone for MSN Healthy Living

1 of 16 Woman at dentist (© altrendo images/Getty Images)

1. If you cross your eyes they'll stay that way

Your mom may have told you this as a child, making you forever frightened at looking down the bridge of your nose. "It's simply not true," says Dr. Benjamin H. Ticho, associate professor of ophthalmology at the University of Illinois Eye & Ear Infirmary.
Looking at your nose creates normal convergence (the amount the eyes rotate toward each other to view a near object), says Ticho. "In crossed eyes, one eye looks straight and the other looks crossed." Crossed eyes occur more often in children (find out more) but only in extreme situations in adults (i.e., stroke, Graves’ disease).
Find: Learn more about crossed eyes, one form of a condition called strabismus
2 of 16 Girl crossing eyes (© Jon Anderson/Flickr/Getty Images)

2. Reading in the dark will ruin your eyes

Reading by flashlight in the pitch dark won't ruin your eyesight, but it will make it harder to read, says Ticho. Your eye contains two types of photoreceptors (in the retina): rods and cones. Cones enable you to read and see colors (find out about color blindness) and rods detect motion in your peripheral vision and enable you to see in dimmer light (read about poor peripheral vision).
"One reason you can't read with your peripheral vision is because you're using your peripheral retina, which is mostly rods," says Ticho. When you turn the lights off, your eyes also switch from the cones to the rods. Rods don't work as well for reading, but you won't do any harm aside from a little eye strain.
3 of 16 Person reading (© Keith Goldstein/Getty Images)

3. Eating carrots helps your vision

Unless you're deficient in vitamin A, eating carrots likely won't make a difference in how well you see, says Ticho. "For the vast majority of people who eat a good diet, eating carrots or other vitamin-A-containing vegetable isn't going to make their photoreceptors (cells in the retina) work any better."
However, a healthy diet containing carrots is shown to reduce the progression of macular degeneration, the leading cause of blindness in the above-60 age group, says Dr. Sandy T. Feldman, an eye surgeon who is the medical director at ClearView Eye & Laser Medical Center in San Diego. "In addition to beta carotene, carrots contain lutein and zeaxanthin, important antioxidants for eye health," says Feldman.
4 of 16 Woman with carrot (© Asia Images Group/Getty Images)

4. We use only 10 percent of our brains

On days when you can't recall a name or phone number, it's tempting to wish for more brain power. Only we're using all that we have, just not all at once, says Dr. Marie Pasinski, staff neurologist at Massachusetts General Hospital, faculty member at Harvard Medical School and author of “Beautiful Brain, Beautiful You” (Hyperion, 2010).
"Think of your brain as a computer with special programs and software to allow it to perform an amazing array of tasks," says Pasinski. At any given time, not every single application is in use. When we are focused on a specific task, the parts of the brain needed for that task become more active.
5 of 16 Brain activity (© Corbis)

5. If you swallow your gum, it'll take 7 years to digest

Swallowing your gum on that amusement park ride last summer does not subject you to a gummy digestive tract for seven years, says Dr. Richard Desi, a gastroenterologist with the Institute for Digestive Health and Liver Disease at Mercy Hospital in Baltimore.
"This is certainly a myth. A portion of gum is indigestible, and like any indigestible substance that is consumed, it will simply pass through the gastrointestinal tract and be evacuated." The digestible ingredients in gum (find out more about what's in gum) do not take any longer than other foods to digest. And the indigestible portion does not "stick" around one's intestines for years, says Desi.
6 of 16 Gumball machine (© Corbis)

6. You can tell the gender of the baby by the way the mom carries the child

This oft-repeated myth says if a pregnant woman carries high she's having a boy; if she's carrying low and wide it's a girl. "This myth has been around forever, but there's no good data to show there's any truth in it," says Dr. Robert Atlas, chair of the Department of Obstetrics at Baltimore's Mercy Medical Center. "There's no reliable way to predict the gender of a baby by looking at a woman. Besides, anyone has a 50-50 chance of being right."
7 of 16 Pregnant woman (© Image Source/Getty Images)

7. Professional removal of plaque loosens your teeth

The opposite actually holds true, says John Koutsoyiannis, DDS, founder of SoHo Smile in New York. "The reality is if you leave plaque on your teeth it turns into tartar (what's another word for it?). Not removing it can loosen your teeth." If a person hasn't had her teeth cleaned in a long time and her teeth are compromised, she may feel spaces between the teeth once the tartar is removed, which may make them feel loose, says Koutsoyiannis. "Or, in cases of severe periodontal disease, the tartar may be holding the teeth together and [they] were loose all along."
8 of 16 In the dentist's chair (© Thinkstock Images/Comstock Images/Getty Images)

8. A cold shower can dampen libido

Showering with cold water may shock you out of sexual frustration, but there's no physical reason it should do much to dampen your libido, says Atlas. "The shock to a man's body triggers the cremasteric reflex, however, which causes a muscular pulley action that pulls a man's testicles up into his body to seek a warmer environment, which could temporarily dampen libido." (A study from 1993 done by the Thrombosis Research Institute in England actually found an increased number of virus-fighting white blood cells and increased testosterone in men after a cold shower. So the opposite may actually hold true.)
9 of 16 Cold shower (© Peter Cade/Getty Images)

9. Only women have a biological clock

A woman's biological clock may tick louder, but a man's fertility also decreases with age, according to research from Johns Hopkins University (read more about biological clocks). While women are born with all the eggs they'll have for life, men can manufacture sperm throughout their lifetime. But the quality of their genetic material decreases. "Men over 45 years old have a higher risk of fathering children with genetic abnormalities," says Atlas. "This occurs most often in single-gene defects such as Huntington's disease (read more about the neurological disorder) as well as muscular dystrophy." Research from Mount Sinai Medical Center in New York also shows that men older than 45 have twice as much damage to their sperm as men under 30.
10 of 16 Woman's clock ticking (© Matthieu Spohn/Ès Collection/Photolibrary)