In search of the safe suntan
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
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
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