For years, the official word on tanning has been...don't. Health organizations have driven home the message that even if we think a suntan looks healthy, it's not, and that the sun exposure needed to get the tan increases your chances of getting skin cancer.
Researchers at the Harvard-affiliated Dana-Farber Cancer Institute in Boston have conducted a series of experiments that put tanning in a different light. A suntan, they say, is the body's best effort to fend off the known cancerous effects of ultraviolet (UV) light, the invisible portion of the light spectrum that comes in short, energy-packed wavelengths that penetrate the skin and mutate DNA.
The Harvard researchers are emphatically on the side of sunscreen and avoidance of excessive sun or other UV exposure. But they're also looking for ways to harness the "tanning pathway" that might give fair-skinned people the protective benefits of having a tan without going through the hazards of getting one.
How we tan
The conventional wisdom about how a suntan comes about has been that when UV light strikes cells in the skin called melanocytes, the cells produce the brownish-black pigment called melanin, which darkens the skin. So while a tan itself wouldn't cause cancer, it's a sign of UV exposure that almost certainly does.
But all along there's been some confusion, because it's well documented that people with dark skin, as well as those who tan easily, are less likely to get skin cancer than fair-skinned people. If a tan signals possible skin damage, why is it also associated with a lower risk of skin cancer? Might a tan be protective?
Experiments have shown that tanning is a more circuitous process than previously thought. It starts when UV light provokes keratinocytes, the main cells of the upper epidermis, to release hormones that stimulate melanocytes, which lie deeper in the skin than the keratinocytes. The melanocyte-stimulating hormones latch onto receptors located on the melanocytes, more or less putting the key into the ignition of melanin production. But rather than hoarding the pigment, the melanocytes selflessly send much of it back to the keratinocytes, creating a tan.
When the melanin enters a keratinocyte, it concentrates over the nucleus — where the DNA, the cell's genetic material, is located. "It actually collects on the sun-facing side of the cell," notes Dr. David Fisher, director of the Melanoma Program in Medical Oncology at Dana-Farber. "We don't fully understand the mechanisms at work...but under a microscope, the pigment forms into these super-efficient little umbrellas protecting the nuclei." That protection from UV light may prevent mutations that could result in skin cancer.
"The trigger for tanning — UV radiation — is absolutely damaging and absolutely carcinogenic," continues Dr. Fisher, noting that the protection afforded by melanin is not absolute. "But tanning itself appears to be an adaptive response to harmful stress."
Tan for the tanless
That's the story of tanning, but what about people who don't tan? Dr. Fisher's lab and others have conducted experiments that suggest the melanocytes of redheads (who are nontanners) have a variant form of an important receptor. When melanocyte-stimulating hormones bind to those receptors, melanocytes don't produce the dark melanins that give people a tan. So, instead, the skin cells are left with melanin that's reddish yellow in color and — unlike the darker melanins — this version seems to offer little in the way of protection against UV radiation.
Dr. Fisher and his colleagues decided to find out whether it might be possible to work around the receptor that doesn't produce dark melanin. He treated red-haired lab mice (a model for humans who don't tan) with a topical preparation known to raise levels of the next compound in the tanning pathway. It worked. Without any UV exposure the mice tanned a deep, dark brown. Moreover, their tans had all the protective characteristics of a regular, UV-induced tan.
So, if tans are protective, should we toss our SPF 45 and become sun worshippers? Definitely not. The only safe tan would be one produced by activating the skin's tanning process without running the risk of the DNA damage that occurs with exposure to UV light, either naturally from the sun or artificially at a tanning salon.
But should easy, dark tanners seek out a tan for its protective value? The answer is no, because the UV light needed to get that tan can cause skin cancer. It's unclear if truly safe UV exposure can ever be achieved.
For now, your best bet is to avoid excessive UV light exposure — especially if you're blond or redheaded and don't tan well, but also if you do. And use sunscreen. It protects against sunburn — and severe sunburn is thought to be a risk factor for melanoma. The protective value of any sunscreen depends on how you use it and, in particular, whether you use enough. To get the full benefit, apply sunscreen before going outside, and use about two to three tablespoons for your whole body. You should also reapply sunscreen every two hours or after going in the water.
July 2007 update