Sun screen.

When summer comes, I get sun crazy. I like to eat on the patio and lie on the beach. I walk and bike everywhere. I even bring my work outside. Soaking up the sun feels so good--as long as I'm wearing sunscreen and a hat.

When I was younger, I played in the sun without worry. Now that I'm 30, I realize how important it is to protect myself. That's because the same ultraviolet (UV) rays that make us warm and tan also harm the cells in our skin. You can't see the damage when you're young, but its effects often show up decades later.

After years of tanning, the skin gets wrinkled, leathery, and, worst of all, prone to skin cancer. The disease is directly linked to UV exposure, says Mandeep Kaur. She's a dermatologist at Wake Forest University School of Medicine in Winston-Salem, N.C.

As young people flock to beaches and tanning salons, skin cancer is becoming more common and appearing at younger ages, Kaur says.

"We used to see only older and middle-aged people with skin cancer," she says. "These days, we see people in their 20s or 30s."

Tanning dangers

Kaur and her colleagues reviewed a large number of studies about skin cancer and UV light. The disease, they found, is the most rapidly growing cause of cancer deaths in the United States.

Even so, doctors rarely warn their young patients about the dangers of tanning.

What your doctor should tell you is that your skin is the largest organ in your body. It keeps your stomach and other organs from spilling out. And it keeps germs from getting in. Skin allows you to feel pain, heat, cold, and other sensations. And through sweat, it rids your body of extra water and salt. Can you imagine life without it?

Although our skin works hard to protect us, few people work to protect it. The sun's UV rays are the biggest threat because they damage the genetic material DNA in the cells of your skin. Damaged, or mutated, cells are supposed to kill themselves, but sun-damaged skin cells eventually become cancerous and multiply out of control. They produce abnormal growths called tumors.

The tricky thing is that this process can take 30 or more years to become evident.

"It's surprising how long it takes," says Meenhard Herlyn, a tumor biologist at the Wistar Institute in Philadelphia. "Even if kids have big, blistering sunburns every summer, they're fine while they're kids."

Skin cancer

There are two categories of skin cancer. Nonmelanoma tumors develop in the outermost layer of skin. They usually appear on the head, neck, and other exposed areas. There are about 1 million new cases of nonmelanoma in the United States each year, according to the American Cancer Society. Doctors can easily remove most of these cancers if they catch them early.

The second type of skin cancer is melanoma. It is less common than nonmelanoma cancer. There are only 60,000 new cases a year in this country. However, melanoma is far more likely to spread to other organs and become deadly. Melanoma affects the cells in your skin that produce pigment, or color, that makes you tan. These cells are most active when you're young, so getting sunburns during childhood puts you at especially high risk.

"If you have more than five blistering sunburns while you're under 15," Herlyn says, "it increases your risk for getting melanoma three- to fivefold."

All types of skin cancer occur most often in people who have red or blonde hair, freckles, or pale skin that burns easily. People with naturally dark skin rarely get skin cancer.

Skin cancer treatment usually involves surgery to remove damaged cells, but new approaches are in the works. The most promising leads come from studies of internal signals that cancer cells use to stay alive.

"We're slowly getting to know what makes melanoma cells tick," Herlyn says. If researchers can block the important signals with drugs, the bad cells might die.

Herlyn's coworkers, for example, are working on a melanoma vaccine that would help a patient's immune system recognize and attack skin cancer cells. Other scientists are creating lotions that could help cells repair themselves.

Sunning safely

The best way by far to fight skin cancer is to not get it in the first place. That doesn't mean you have to stay inside all the time. You just have to learn how to be sun savvy.

The American Academy of Dermatology recommends wearing sunscreen (SPF 15 or higher), sunglasses, wide-brimmed hats, long-sleeved shirts, and long pants whenever possible. Avoid direct sunlight when it's at its strongest-between 10 a.m. and 4 p.m. Be careful near snow, sand, and water, which create strong reflections. And avoid tanning beds.

These steps may seem extreme if you live in a place where tanned skin is considered attractive. But if you want a wrinklefree, cancerfree future, it may be time to think about the cost of "beauty" that doesn't last.

"If you want to be healthy," Kaur says, "you have to have good skin."