You’ve heard them before: Eat your veggies. Get eight hours of sleep each night. Don’t cross your eyes, or they’ll stay that way. Many health rules are grounded in science and should be followed as part of a balanced and healthy lifestyle, but others? Not so much. Here are six popular rules that aren’t as hard-and-fast as you might think.

  1. Don’t crack your knuckles. The myth is that this habit will cause arthritis. It may be annoying, but no medical studies prove cracking or popping your fingers will lead to arthritis. However, some doctors say cracking your knuckles repeatedly may hurt your fingers in other ways (besides driving your coworkers crazy), so it’s best to avoid the habit. Ever wondered where the popping sound comes from? When you stretch your fingers you pull the bones, creating an air bubble around the joints. When the bubble bursts, it makes a sound.
  2. Don’t go outside with wet hair. It may make you feel chilly (wet hair doesn’t insulate well), but it won’t make you sick. Colds are caused by a virus that is usually spread by droplets from someone’s cough or sneeze. To avoid the virus, you’re better off washing your hands often and avoiding crowded places or close contact with someone who’s sick. What does make you more vulnerable to a cold virus: fatigue, stress, and certain bad allergies.
  3. Don’t swim after you eat. Sorry, Mom, but there’s no evidence that this causes cramps, which could possibly lead to drowning. While it’s true that eating diverts some blood to the digestive system, most experts agree your body can still provide enough blood and oxygen during exercise to keep cramps from happening. Eating a big meal may make you feel too full to knock out a bunch of laps, but it won’t make you drown.
  4. Drink eight cups of water a day. As long as you’re drinking enough so that you don’t feel thirsty, you urinate often, and your urine is nearly colorless, you’re probably getting enough water. And remember that magic “eight cups a day” includes water you get from foods and other beverages, and those help you gain other nutrients, too. While water is necessary, some healthy alternatives to H20 include broth-based soups and water-laden produce such as grapes, cucumbers, and melon.
  5. Avoid reading in dim light. You may get a headache and strain your eyes, but experts say poor lighting will not cause permanent damage to your eyesight. Ditto for sitting too close to a television or computer screen. To reduce eye strain, sit at a comfortable distance and take breaks often—at least every 20 minutes.
  6. Use birth control that follows your monthly cycle.Traditional birth control pills are based on a 28-day cycle. The pills have reproductive hormones you take for the first 21 days, followed by a placebo for the next seven days, during which you have your period. In the past, doctors sometimes adjusted the dosage for women with painful or heavy periods. But with the advent of extended-cycle birth control pills, you can skip your period altogether or have it just a few times a year. Talk to your doctor to see which option is right for you.