Think you've heard it all when it comes to the dangers of the sun? Sure, you know that tanning salons are unhealthy, and you should avoid the sun during peak hours and wear sunscreen. But that's just the start—and what you don't know can literally kill you.

There are over one million new cases of skin cancer diagnosed in this country each year, with nearly one in five people expected to get skin cancer in their lifetime, according to the skin cancer foundation. "People don't realize that it's one of the most common forms of cancer," says Dr. Ronald Moy, director of dermatology at the California Health and Longevity Institute. "And really, it's preventable."

To practice prevention, start by conquering these dangerous habits you may not even realize you're guilty of...