But, how true are they?
Prevention magazine looked into a bunch of the most popular ones and reported the results in its September issue.
On The Early Show Tuesday, Prevention Editor in Chief Liz Vaccariello filled in viewers about several of them.
To see the complete article in Prevention, click here.
Here's some of what the article says about the ones she talked about:
It's safe to follow "the five-second rule" for food dropped on the floor.
It's probably not even safe to follow a 1-second rule: The transfer of bacteria from a contaminated surface to food is almost instantaneous-or, at the very least, quicker than your reflexes.
BOTTOM LINE: If you've fully sterilized your floors, go ahead and serve a whole meal under the table. But there are 76 million cases of food-borne illness annually in the United States according to the CDC, so barring that level of cleanliness, avoid eating food dropped on the floor.
Cell phones are dangerous to use in hospitals because they can interfere with medical equipment.
VERDICT: Jury's out
There's a chance that a cell phone call in the wrong spot can cause ventilators, syringe pumps, or even signal pacemakers to pulse incorrectly, according to a 2007 Dutch study, which found that 43% of the phones caused electromagnetic interference with critical-care equipment. However, a Mayo Clinic study a year prior to this found no instances of interference and advised hospitals to drop or revise their cell phone bans.
BOTTOM LINE: Use a designated cell phone area in a hospital , which most now offer -- or use a call as an excuse for a walk-and-talk outside for some fresh air and exercise. If that isn't possible, have a calling card available to use a hospital pay phone.
Cracking your knuckles can cause arthritis.
If you're suffering from osteoarthritis in your hands, it certainly has nothing to do with this nervous tic. One study at the former Mount Carmel Mercy Hospital in Detroit compared 74 people (age 45 and older) who had been chronic knuckle crackers for decades with 226 who always left their hands alone; researchers found no difference in the incidence of osteoarthritis between the two groups.
BOTTOM LINE: Get to the bottom of what's causing the nervous tic in the first place -- you may crack your knuckles more often at work than at home, for example -- and address those sources directly.
Cola-type soft drinks can damage your kidneys.
Despite their global popularity, there's nothing remotely healthy about cola beverages: Drinking 16 ounces or more daily (whether diet or regular) doubles your risk of chronic kidney disease, according to a recent NIH study of more than 900 people. Experts suspect the ingredient phosphoric acid may be the culprit.
BOTTOM LINE: If you're going to indulge in an occasional soda, go for Sprite, 7-Up, Fresca, and the like. The NIH study found that non-cola drinks didn't have the same impact on the kidneys. But you'll be better off if you skip soda altogether.
"Double-dipping" spreads germs from one chip to another.
A double-dip deposited thousands of saliva bacteria into the dip -- and of those, 50 to 100 were later transferred through the dip to a clean cracker, presumably destined for another guest's mouth. Still unknown, however, is how long such bacteria can survive in the dip or if they can actually infect another dipper upon ingestion.
BOTTOM LINE: You better be pretty comfy with your party guests. Eating from a dip after someone has dipped twice is basically the same as kissing that person.
Sitting too close to the TV is bad for your eyes.
Like many electronic devices, TVs ordinarily give off low levels of radiation. Before the 1950's, television sets emitted levels of radiation that after repeated and extended exposure could have heightened the risk of eye problems in some people. But modern televisions are built with proper shielding, so radiation is no longer an issue. So while this might have been an issue for your grandmother's generation who gives you these warnings, it is no longer true today.
BOTTOM LINE: Sitting closer than necessary to a TV may give you a headache, but it will not damage your vision.