Non-melanoma skin cancers appear to be on the rise among young adults in the U.S., with the biggest increases being seen in women, according to a new study.

Researchers at the Mayo Clinic reported a more than doubling of the incidence of squamous cell and basal cell carcinomas among women under the age of 40 since the mid- to late-1970s, while only a slight increase has been seen among men. The study will appear Wednesday in Journal of the American Medical Association.

The new study did not address the reason for the rise, but experts tell WebMD that they suspect the popularity of tanning beds among young women may be at least partly to blame.

"Generally, about 80 percent to 90 percent of nonmelanoma skin cancers occur around the head and neck, but in the population that we studied there was a higher percentage of tumors occurring on the torso, especially among young women," dermatologic surgeon and researcher of the study Leslie J. Christenson, MD, tells WebMD. "This suggests intentional tanning, either through tanning beds or lying out in the sun."

Skin Cancer Danger: Not Just in Summer

Skin Cancer Most Common After 50

More than a million cases of skin cancer are diagnosed in the United States each year, and roughly 97 percent of these are the nonmelanoma cancers. Basal cell carcinoma is by far the most common type of skin cancer, followed by squamous cell carcinoma.

Nonmelanoma skin cancers are highly treatable if the skin lesion is identified and removed early. They are most commonly seen in people over the age of 50, but Christenson says her experience led her to suspect that the cancers were on the rise in younger people.

"As a dermatologic surgeon, I was operating on more and more younger women," she says. "That is what led us to do the study."

The Mayo researchers found that between the late 1970s and 2003, the incidence of basal cell carcinoma skin tumors doubled among people younger than age 40, with the rise in cases among women accounting for most of the increase.

The rate for basal cell carcinomas per 100,000 people in the mid- to late-1970s was 13.4 cases among women and 23 cases among men. Between 2000 and 2003, the rate was 31 cases for women and 26 cases for men.

Christenson says the increased rates in these tumors among young people points to an overall rise in skin cancers in the near future.

"50 percent of people who have one (nonmelanoma skin lesion) will have a second one within two to three years, and 75 percent of people who have two will have a third," she says.

American Cancer Society skin cancer spokesman Martin A Weinstock, MD, PhD, says the fact that the rise was so much more apparent in women than in men seems to implicate intentional tanning, and especially tanning bed use.

It is clear that women use tanning beds much more often than men do. A recent study showed that girls in their late teens were almost seven times as likely as boys to report tanning with the aid of a tanning bed.

"We can't tell from this report that this is the cause, but it is certainly something that needs further study," Weinstock tells WebMD.

Sun Exposure and Skin Cancer

Tanning Beds to Blame?

But not everyone agrees that tanning beds deserve some blame.

"To jump to this conclusion is just an unfair analysis of the data," Indoor Tanning Association Executive Director John Overstreet tells WebMD. "It is a disservice to our industry and to people who depend on science to make decisions about their lives."

Overstreet added that it is surprising that skin cancers are increasing despite aggressive public health campaigns warning against sun exposure.

"If you accept the fact that sunscreen and an awareness about the dangers of overexposure are now part of everybody's life, then this suggests that other factors might be involved," he says.

Protecting Yourself From the Sun

Though most people now use sunscreen when sunbathing, Weinstock says it is rarely used in the most effective manner. That means:

—Applying a 30 SPF or higher sunscreen 20 minutes before exposure.

—Reapplying 20 minutes after exposure begins when the sun's rays are intense.

—And reapplying periodically after that, depending on the type of sunscreen you use and how active you are.

"It is almost impossible to figure out how often to reapply sunscreen by looking at most (sunscreen) labels," he says. "That makes it very difficult for people who are trying to do the right thing, let alone those who aren't paying much attention."

The American Cancer Society has also borrowed the slogan "Slip, Slop, and Slap" from an Australian skin cancer awareness campaign. The campaign urges people to slip on a shirt, slop on the sunscreen, and slap on a hat before sunbathing, Weinstock explains.

"It is the best way to protect yourself when you are out in the sun," he says.

Visit Web MD's Cancer Health Center

By Salynn Boyles, reviewed by Brunilda Nazario, MD

SOURCES: Christenson, L.J. Journal of the American Medical Association, Aug. 10, 2005; vol 294: pp 681-690. Leslie J. Christenson, MD, clinical researcher and dermatologic surgeon, Mayo Clinic, Rochester, Minn. Martin A. Weinstock, MD, PhD, professor of dermatology and community health, Brown University, Providence, R.I.; chairman, American Cancer Society Skin Cancer Advisory Group; chief of dermatology, VA Medical Center, Providence, R.I. Geller, A.C.Pediatrics, 2002. John Overstreet, executive director, Indoor Tanning Association.