Spring break = cancer season?
As you pack your bags for Ft. Lauderdale and get set for an overdose of sun 'n fun, we hate to act like a wet blanket. But have you thought about the ultraviolet rays in that blessed sunshine -- and what they are doing to your skin?

Sure, you've read the warnings: Stay out of the sun. Slather on the suntan lotion (don't forget the soles of your feet). Wear a suit of armor.

But what's the reality of skin cancer? Which type is most dangerous? Can you realistically protect yourself from the sun during a fast game of beach volleyball?

Skin cancer is the most common of all cancers, accounting for more than 40 percent of cases. More than one fifth of Americans will develop skin cancer at some point. More than a million Americans will be diagnosed with skin cancer this year, according to the American Cancer Society. Since 1981, the incidence of malignant melanoma -- the most deadly form -- has crept up by about seven percent a year. Skin cancer, mainly melanoma, will kill more than 7,000 Americans this year.

Breaking news
The skin cancer story is largely a story of sunlight, which causes most, but not all, cases of the disease. Knowing your enemy is the best way to start the battle against the sun.

The dangerous part of sunlight is the waves in high-energy ultraviolet (UV) region. These come in three flavors, ranging from low to high energy: UV-A, UV-B, and UV-C.

UV-A rays penetrate deepest into the skin. While it's unclear how many skin cancers are attributable to UV-A, they are not blocked by glass or most sunscreens.

UV-B causes most sunburns and, experts think, most skin cancers. Some UV-B is partly absorbed by high-altitude ozone. It is blocked by window glass, most sunglasses, and (to varying degrees) sunscreens. A few insidious rays, however, penetrate the top layer of skin and cause aging, immune-system damage and cancer.

UV-C are entirely absorbed by ozone molecules in the atmosphere.

As you can see, most of the concern focuses on UV-B. These rays penetrate the epidermis (the top layer) and damage cells. If UV-B passes through a cell nucleus, it can strike DNA molecules in the chromosomes, breaking them or forming abnormal chemical bonds. In severe cases, entire chromosomes can be reshuffled. Sunlight is most damaging in childhood, when cells are dividing rapidly -- creating opportunities for persistent mutations.

Still, much of the DNA damage is harmless. The body has evolved remarkable mechanisms that constantly monitor and fix DNA, and many of the unrepaired cells commit suicide.

Sunlight's ultraviolet radiation strikes where you are most vulnerable: DNA. Graphic from NASA

But if mutated cells divide without normal limits, that's cancer.

Skin cancer, like other tumors, can spread through metastasis, in which diseased cells hitch a ride in blood or lymph to other organs. Before metastasis, many skin cancers are easy to treat by surgical removal or topical chemotherapy.

The three scourges
Skin cancer has three faces: basal cell carcinoma, squamous cell carcinoma and melanoma. Basal cell and squamous cell carcinomas account for the vast majority of skin cancers. Thankfully, they are the least deadly: When treated early, the cure rate is upwards of 95 percent. Both cancers are likely related to the lifetime sunlight exposure.

Basal cell carcinoma is a slow-growing cancer that rarely metastasizes and is almost never fatal. These growths begin in the lowest layer of the epidermis (called the basal layer, and made, appropriately, of basal cells). Basal cells continually divide to replenish the 2 square meters of surface skin that is continually weathering away.

About 75 percent of skin cancers are basal cell carcinomas, which usually develop on sun-exposed areas like the head and neck. They sometimes appear as a red patch of skin or a pearly, translucent bump. They can also be an irritable open sore that doesn't heal, or a scar-like lesion.

Squamous cell carcinoma is less common. In rare cases, it can spread and be life threatening. These cancers develop in higher levels of the epidermis, where cells grow tough to protect the body. Accounting for one-fifth of all skin cancers, squamous cell carcinoma is directly related to sun exposure. It occurs on the most sun-exposed areas, such as the head and neck. Squamous cell carcinoma can appear as a scaly red patch that sometimes scabs or bleeds; an open sore that refuses to heal; or a raised, wartlike growth.

Melanoma is a different story. Far more severe than other skin cancers, it is also the least common. Melanoma occurs in the pigment-producing cells of the epidermis. These so-called melanocytes produce melanin, the pigment that darkens skin and helps protect deeper cells from UV. Melanocytes also make benign growths called moles. Melanoma occurs in varying shades of brown or black or in multicolored patches of red, white, and blue.

Melanoma can be deadly, but it is often curable if caught early. It is also the least predictable skin cancer. It can occur anywhere, not just in sun-exposed skin. About 70 percent of melanoma cases develop in normal skin, while only 30 percent develop in moles. It can occur anytime, and is not strongly associated with lifetime accumulation of sun exposure. Some experts believe melanoma is linked to a few severe sunburns in early life, but others say this link is tenuous and almost impossible to prove.

Oddly, melanoma is not as tightly correlated with sun exposure as other skin cancers. Even more oddly, it's not proven that sunscreen can protect against melanoma. We'll return to that issue...

Protect thyself
If you've read much about skin cancer, you know that early detection matters. Beware of large moles and moles with irregular borders or mingled tones. Keep a careful watch for changes in all blemishes. You probably know that the darker your skin, the lower your risk. That's because dark-skinned people have more melanocytes, and thus more protective melanin. But no one is invulnerable, and skin cancer can take so many forms that it can be difficult to recognize.

By all accounts, everyone should be aware of the ABCD warning signs of skin cancer: (Asymmetry, Border irregularity, Color variation, Diameter larger than a pencil eraser). But what if you have lots of moles, and most are funny-shaped or multicolored? What if there are too many to keep track of? Chances are you should get checked by a dermatologist. (Chances are that the modestly moley should also get checked, too.)

In between self-checks and doctor's visits, remember these precautions. Since skin cancers are linked to severe sunburn, experts urge you to minimize your sun exposure. But even for those who are reluctant to adopt a vampirish existence and stay indoors from 10 a.m. to 4 p.m., there is hope. For one thing, protective clothing and sunscreen help to prevent burns and reduce cumulative exposure.

However, there are some further cautions. For one thing, most people just don't slather heavily enough. "The average person who applies sunscreen only puts on about one-fifth of the amount used in testing to establish SPF [sun protection factor rating for sunscreen]," says Eric Kilber, a resident in the University of Wisconsin-Madison department of dermatology, "so if you put on SPF 30, it's probably more like SPF 6. It should be generously applied. A couple of small blobs will not cover your face trunk and arms."

Secondly, he urges caution in the wet tee-shirt department. Not just any shirt will keep the rays at bay. "A white tee-shirt is not much protection especially if it gets wet," Kilber says. "Tightly woven, bright-colored clothes, please."

Skin cancer: The ozone zone.

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