That’s easy: the sun. Ultraviolet (UV) rays in sunlight are by far the top cause of skin cancer. UV rays damage DNA in skin cells. If the genetic damage is severe, a normal skin cell begins to grow in an uncontrolled way, which is what cancer is. This direct link between sun exposure and skin cancer is why the medical community is so determined to get you to use sunscreen when outdoors. And yes, tanning booths can contribute skin cancer. There are other causes, but they are far less common: having an impaired immune system that doesn’t protect your skin from germs; exposure to unusually high levels of X-rays; and contact with toxic chemicals, such as arsenic or hydrocarbons in tar, oils, and soot.

• Skin cancer is the most common of all human cancers. More than 2 million people are diagnosed with the disease each year in the United States.
• Some experts say 80 percent of lifetime sun damage occurs before age 18. In fact, one blistering sunburn in childhood more than doubles a person's chances of developing melanoma later in life.
• Between 40 and 50 percent of Americans who live to age 65 will have at least one skin carcinoma -- the precursor to skin cancer.
• Skin cancer affects people of all skin tones, including those with darker complexions, but people with fair skin, blond hair, blue or green eyes are most susceptible.
• On an average day, more than one million Americans use tanning salons. Users are 2.5 times more likely to develop squamous cell carcinoma (a precursor to skin cancer) than nonusers.

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