According to the Skin Cancer Foundation, about one in five Americans
will develop skin cancer at some point in their lives. One form of skin
cancer is melanoma. It's caused when melanocytes (the pigmenting cells
in the skin) become abnormal and mutate into cancerous cells.
Last year, about 114,900 new cases of melanoma were expected to be
diagnosed in the U.S. It's the most common type of cancer among those 25
to 29. Although melanoma causes less than five percent of skin cancers,
it accounts for more than three-fourths of all skin cancer deaths.
At least 65 percent of all melanomas are related to exposure to the
sun's ultraviolet (UV) rays. Experts say one blistering sunburn during
childhood or adolescence doubles the risk for melanoma.
The Role of UV Rays
Sunlight contains three main types of UV light. UVA rays are the
longer wavelengths (320 to 400 nm) which penetrate deeply into the skin.
UVB rays (280 to 320 nm) are absorbed into the epidermis (the outer
layer of skin). UVC rays (less than 280 nm) are of the shortest
wavelength. However, these rays are mostly absorbed by the ozone layer
and oxygen, so they have little effect on the skin.
When the skin is exposed to sunlight, the pigmenting cells react by
making more melanin. Arthur Balin, M.D., Ph.D., Dermatologist practicing
in Media, PA, says this response is actually a sign that the DNA in the
skin cells has been damaged. So a tan is really a mark of injury to the
skin cells, which Balin describes as a sort of "bleeding".
Studies show UVB rays can cause significant mutations in cellular
DNA, accounting for 80 to 90 percent of sunlight's DNA skin damage.
However, Balin says when researchers studied sunlight exposure in
melanoma patients, the investigators found that most of the cancers were
related to UVA exposure. Researchers say UVA rays are not readily
absorbed by cellular DNA, and thus do not directly damage the cells.
Instead, UVA light produces reactive oxygen species, free radicals that
can ultimately damage cellular DNA.
Health experts say the best way to reduce risk for skin cancer from
UV rays is to stay out of the sun as much as possible (especially during
peak daytime hours), wear protective clothing (hat, long-sleeved shirt
and long pants), avoid tanning beds and wear a generous amount of
sunscreen when outdoors (even on cloudy days, since sunlight can
penetrate the clouds).
Balin cautions that not all sunscreens are equal. Some only provide
protection from UVB. Instead, look for a full-spectrum product, one that
provides protection from both UVA and UVB. Look for the ingredients,
zinc oxide or titanium dioxide, on the label. These agents physically
block the UVA rays.
The FDA has recently passed a ruling allowing manufacturers of
sunscreens that pass testing for effective UVA and UVB protection to
label the bottles as "broad spectrum." The new labels will help
consumers make better choices for sun protection and, hopefully, reduce
the risk for skin cancer. Look for the new labels to appear by 2012.
Research compiled and edited by Barbara J. Fister
AUDIENCE INQUIRYFor general information on melanoma, the dangers of tanning or sun protection:
American Academy of Dermatology, http://www.aad.org/skin-care-and-safety/skin-cancer-prevention
American Cancer Society, http://www.cancer.org
Centers for Disease Control and Prevention, http://www.cdc.gov/cancer/skin
National Cancer Institute, http://www.cancer.gov
The Skin Cancer Foundation, http://www.skincancer.org
BIBLIOGRAPHYIf you need a list of the research titles supporting this story, please contact Barbara Fister at (610) 395-1300 ext. 238.