You've heard it before -- cell phones cause cancer, going on the pill can make you fat, and cold weather can cause you to catch a cold. But are these claims fact or fiction?

Last year alone, Americans used more than 2-trillion cell phone minutes. But can all that time with the gadget next to your head cause brain cancer? "There's no evidence to show that cell phones cause cancer. The radiofrequency that the cell phones emit is much lower than some of the standard devices that we use everyday in our daily lives such as microwaves," says Dr. Vijay Reddy, Hematologist/Oncologist at the Florida Hospital Cancer Institute in Orlando, FL.

Another common belief -- many think once brain cells die, they're gone for good. But there's good news! We DO grow new brain cells. "What we think happens is that people who really keep their brains very active build up a cognitive reserve," says Dr. Cynthia Holzer, Director of Geriatric Education at the Roger Williams Medical Center in Providence, RI.

The best way to do it? Doctors say exercise for 30 minutes, read or play a musical instrument.

Gaining weight is a big fear for many women. Some fear the scale so much they won't take birth control pills. "The modern birth control pills we have do not cause any weight gain, weight loss or any change in weight at all," says Dr. D. Ashley Hill, Medical Director at the Loch Haven OB/GYN Group at Florida Hospital in Orlando, FL.

Today's birth control pills have 20 to 30 micrograms of estrogen while oral contraceptives in the 1960s had up to 150 micrograms.

With the cold weather season behind us, you'll probably be tossing out your old cold medicine. But is cold weather really to blame for your sore throat and runny nose? No! This too is a myth.

"The fact that children get sick is a fact of life," says Dr. Vinny Chulani, Pediatrician at the Arnold Palmer Hospital for Children in Orlando, FL.

Experts say the only way to get sick is through direct contact with the virus, like by coughing or sneezing.

Here are some other fun facts you may have already heard before: Toothpaste can zap acne by absorbing oil, and poppy seed muffins can make you fail a drug test, because the seeds contain small traces of opiates found in drugs like morphine and codeine.