Mackenzie R. Wehner, from the Stanford University School of Medicine in California, and colleagues performed a meta-analysis of 12 studies examining the association of indoor tanning with non-melanoma skin cancer, which included 9,328 cases of non-melanoma skin cancer (7,645 basal cell carcinomas and 1,683 squamous cell carcinomas).

The researchers found that, compared with those who never used indoor tanning, those who had ever used indoor tanning had a higher risk of squamous cell carcinoma (summary relative risk, 1.67) and basal cell carcinoma (summary relative risk, 1.29). They estimated that, for the United States, 8.2 percent of squamous cell carcinoma cases and 3.7 percent of basal cell carcinoma cases could be attributed to indoor tanning, corresponding with approximately 170,000 cases of non-melanoma skin cancer each year. The risks were higher for those using indoor tanning before 25 years of age, with a relative risk of 2.02 for squamous cell carcinoma and 1.40 for basal cell carcinoma.

"Indoor tanning is associated with a significantly increased risk of both basal and squamous cell skin cancer," Wehner and colleagues conclude. "This modifiable risk factor may account for hundreds of thousands of cases of non-melanoma skin cancer each year in the United States alone and many more worldwide."

One author is a consultant for Genentech.

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