Do you believe in the five-second rule, especially when your grandchild drops that same banana on that same germy floor for the third time in five minutes?

Do you believe your dog's mouth is cleaner than yours? Do you believe you should wait an hour after eating a meal before going swimming? A pair of new books skewer many of the medical myths perpetuated by moms and grandmoms through the ages, and are even being passed down by your doctor today.

Because scores of medical questions -- in the absence of research -- haven't been answered, some doctors still rely on old, and often erroneous, information their mentors shared with them long ago without questioning its validity, experts say.

If your Spider-sense is tingling after hearing some questionable advice at the doctor's office or coming from your grandma across the kitchen table, it's best to ask where they got their facts, albeit respectfully.

What follows are a few of the best medical "whoppers" still alive after all these years. Check out the links below for too many more.

1. It's dangerous to wake a sleepwalker.

2. A teething baby is more prone to fevers.

3. The average human uses 10 percent of his/her brain.

4. Swallowing chewing gum can be hazardous to your health.

5. Closing your eyes during a sneeze keeps them from falling out.

USA Today May 26, 2009

Los Angeles Times May 28, 2009

Newsweek May 27, 2009

British Medical Journal, Vol. 335, p. 1288-1289, December 22, 2007