The researchers suggested use of the devices be limited to adults, and anyone who uses a tanning bed perhaps should be required to sign a consent form acknowledging the risks.
The study, published in the Journal of the National Cancer Institute, is one of several that strongly link the use of tanning lamps with skin cancer.
Dermatologists are not surprised by this -- in order for the skin to tan it has to be damaged. Tanning is the skin's response to the ultraviolet rays given off by the sun and tanning lamps and beds.
"Tanning is a response to injury," Dr. Steven Spencer, a Dartmouth medical school dermatologist who worked on the study, said in a telephone interview. Sunlight also causes wrinkles, age spots and thinning skin, as do sunlamps, he said.
About 1 million Americans are diagnosed annually with skin cancer. About 80 percent are basal cell; 16 percent squamous cell, and 4 percent are melanoma, the most serious form of skin cancer.
Spencer, Margaret Karagas and colleagues interviewed 603 people who had just been diagnosed with basal cell carcinoma and 293 with squamous cell carcinoma. Melanoma patients were not included in the study.
They also spoke to 540 people who did not have skin cancer. Everyone they spoke with was between 25 and 74 years old and lived in New Hampshire.
All of the nearly 1,500 volunteers were asked how often they sunbathed, whether they had ever had a sunburn, if they smoked or ever had radiation treatment and whether they used tanning lamps.
Those who said they had used a tanning lamp or sun-bed were 2.5 times as likely to be in the squamous cell carcinoma group, and 1.5 times more likely to be in the basal cell carcinoma group, as those who said they had never used the devices, the Dartmouth team found.
The risk was highest for those who first used the tanning devices before the age of 20, said Karagas. For this group, the squamous cell cancer risk was 3.6 times greater than the controls. The basal cell cancer risk was 1.8 times greater.
"Our findings suggest that the use of tanning devices may contribute to the incidence of non-melanoma skin cancers," researchers wrote.
Joseph A. Levy, vice president of the International Smart Tan Network and a spokesman for the Indoor Tanning Association, however, said the study "is not an indictment of commercial tanning facilities in any way."
He said that occasional sunburn "is a risk factor in all forms of skin cancer and intermittent sunburn is what the tanning industry is trying to stop."
Levy said there are about 25,000 tanning salons in the U.S. He said it is a $5 billion industry patronized annually by about 28 million Americans.
Spencer said his team considered the possibility that people who used tanning beds may have sunbathed as well, thus raiing their risk of skin cancer from the sun. So they accounted for sunbathing in the report.
But, they said, "no other factors, including summer outdoor exposure, sunbathing or sunburns, affected our results."
The very people who are warned to stay out of the sun were the ones most likely to use the tanning devices -- fair-skinned women who burned easily but who sunbathed anyway.
Spencer said those young women may mistakenly believe they are "laying down a base" that will protect them from the sun.
"The problem is that the kind of tan that a fair-skinned person gets is not very protective," he said.
As with sun exposure, the risk of cancer built over time. Those most likely to have developed skin cancer had first used the tanning devices decades earlier.
Levy said the study is not relevant to the modern tanning industry because most of the patients interviewed were exposed to tanning equipment before 1975.
"Indoor tanning facilities did not come into play (in the U.S.) until 1979," said Levy.
Thus, he said, many of the people interviewed for the study must have improperly used home sun lamps. Commercial tanning parlors, said Levy, use calibrated equipment that carefully regulates and controls exposure.
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