For the new study, Qureshi's team collected data at 84,836 women who took part in the Nurses' Health Study. The women lived in different parts of the United States with different levels of UV exposure.
Over the 18 years of the study, 420 women developed melanoma, 863 developed squamous cell carcinoma, and 8,215 developed basal cell carcinoma.
The researchers found that women living in areas with medium UV exposure had a 47 percent increased risk of developing squamous cell carcinoma. Women living in areas where UV exposure was high had a 90 percent greater risk of developing squamous cell carcinoma.
Qureshi said it's not clear why there are differences in risk for different types of skin cancer. "The question is, is melanoma more a disease of genetics as well as exposure to the sun," he said. "It could be more of a genetic disease than squamous cell carcinoma -- that's really the question."
It's also not clear if the same risk factors affect men, Qureshi said, adding that he and his colleagues are examining that question now. He speculated that they will find the same relationship for the various types of skin cancer among men.
One skin cancer expert advises people to protect themselves from the sun, no matter where they live.
"We have a slogan of the American Cancer Society -- slip, slop, slap," said Dr. Martin A. Weinstock, a professor of dermatology at Brown University and a spokesman for the American Cancer Society. "Slip on a shirt, slop on the sunscreen and slap on a hat. That's the advice when you're out in the sun to protect yourself from the damage that leads to skin cancer, no matter where you live."
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