Everyone’s heard the sayings – an apple a day keeps the doctor away, or cracking your knuckles gives you arthritis.

Some of these stories have a foundation in fact. But many prey on general superstitions, said Dr. Andy Leuchter, professor of psychiatry and biobehavioral sciences.

“Human beings love to see cause and effect when they can,” Leuchter said. “It’s a real problem in the field of medicine.”

Leuchter said patients generally like to think they can do something to affect their own health, which explains the widespread popularity of certain health foods or diets that claim to be effective.

This same theory applies to the belief in health myths, often called “old wives’ tales.” It is related to the placebo response – a well-known effect in which 30 percent of patients with a medical illness respond favorably to a placebo, or a pill with no medical properties.

When someone expects a certain action or food to help with a condition, studies have shown that belief does alter the way the brain works, he said. When a patient undergoes treatment that they think is helpful, their brain chemistry changes slightly and can cause the brain to react a certain way.

What they may not know is that symptoms of illnesses naturally wax and wane as the disease runs its course.

Of the range of health myths, UCLA professors helped explain seven common ones.

Myth 1: You’ll catch a cold if you go outside with wet hair: FALSE

While going outside with wet hair may be uncomfortable, colds are actually caused by viruses.

Thus, this habit won’t make someone more susceptible to colds, said Dr. Peter Galier, an associate professor of medicine at the Santa Monica-UCLA Medical Center and Orthopedic Hospital.

But that doesn’t mean that you wouldn’t feel physically cold. By going outside with wet hair, a person would lose much more body heat through the top of their head, than they would have with dry hair.

As a result, the person might show signs of a cold, like shivering, that are actually brought on by their lower physical body temperature.

Myth 2: Cold showers keep you healthy: FALSE

A cold shower might help to wake you up, or stimulate your body after a bad hangover, but there’s no evidence that it will help you fight off illness, Galier said.

Myth 3: You need to use the information stored in your brain, or you’ll lose it: TRUE

If knowledge from a particular part of the brain is not used frequently, the brain will start to store other information there instead.

“All memories fade,” said Dr. Chris Evans, director of the UCLA Brain Research Institute. “Memories are not necessarily forever.”

He said this phenomenon is particularly true for fetus development. If a fetus’ eyes are closed during development, the cortex will not develop correctly.

Myth 4: Cracking your knuckles makes your knuckles bigger, or will give you arthritis: FALSE

The pops and cracks coming from your hand may sound bad. But the noise you hear is actually the sound of gas coming out of the knuckle’s joints.

“The joint is like a little soda can,” said Dr. John Fitzgerald, an associate professor of rheumatology. “When you hyperbend the joint, you stretch the space, and make a bigger volume and gas pops out.”

He said there is no evidence that shows this behavior leads to arthritis, though he added the knuckle was not designed to crack in this manner.

Myth 5: An apple a day keeps the doctor away: TRUE AND FALSE

Apples don’t have a magical ingredient that ensures perfect health.

But through good nutrition, of which eating appropriate servings of fruit is a part, you can probably reduce the amount of time you spend in the doctor’s office.

“The healthier you eat, the healthier you are,” Galier said.

Myth 6: You only use 10 percent of your brain: FALSE

You might only use one part of your brain to complete a task, but the brain is likely used in its entirety throughout the course of the day, Evans said.

Myth 7: Chicken soup helps you fight colds: TRUE

The popular soup contains defensins, small proteins that defend the cell against certain bacteria and viruses, according to research by Dr. Irwin Ziment, a professor emeritus of clinical medicine.

These proteins are released when the chicken is cooked, making this comfort food analogous to some forms of cold medications.