We’ve all heard them before: widely believed health truisms that have been passed down from our parents or grandparents.

But just because they’re age-old doesn’t mean they’ve aged well. Here are ten common medical misconceptions you should reconsider.

Physical Frights

Will a particular behavior cause you harm?

Myth

Cracking your knuckles will lead to joint issues such as arthritis.

Fact

A satisfying habit for some, an annoying one to others—yet it’s not arthritis causing.

Myth

Going outside with a wet head causes a cold.

Fact

Doing so may make you feel colder, but it won’t make you sick; viruses will.

Myth

Reading in dim light will ruin your eyesight.

Fact

At most, this may merely cause eye strain and headaches.

Myth

You need to wait thirty minutes between eating and swimming or risk drowning.

Fact

A waiting period of any length isn’t necessary. Focus on staying hydrated instead.

Food and Drink

What should you consume or not consume, and when?

Myth

Your goal should be eight 8-ounce glasses of water per day.

Fact

Your ideal water intake depends on factors like your body weight, gender, and health.

Myth

Fresh fruit is better than its frozen counterpart.

Fact

Frozen fruit may actually have more nutrients since it is preserved at peak ripeness.

Myth

Sugar causes hyperactivity in kids.

Fact

Sucrose can certainly cause health problems; however, a sugar rush isn’t one.

Myth

If food drops to the floor, you can safely eat it if you retrieve it within five seconds.

Fact

The item gets contaminated almost immediately, so proceed at your own peril.

Myth

Swallowed chewing gum will remain in your gut for seven years.

Fact

Although the sticky substance isn’t digestible, it should pass like any other food.

Myth

Eating before bedtime is bad for you.

Fact

It’s more about what you eat, how much, and how close to bed rather than the act itself.

Call them what you will: myths, rumors, superstitions, or old wives’ tales. The common denominator is that they started as beliefs and then transformed over the years into generally accepted facts. However, don’t hold on to half-truths when it comes to your health—always ask your doctor if you are unsure about whether something from the medical rumor mill is actually authentic.