Sexual orientation may be a factor in a person's risks of skin cancer and of using indoor tanning devices, suggests a new study.

Gay and bisexual men were up to six times more likely than straight men to use indoor tanning devices and to experience skin cancer while lesbian and bisexual women were about half as likely as straight women to do either, researchers found.

"Unfortunately, we weren't able to directly prove a link between indoor tanning and an increased risk of skin cancer," said Dr. Matthew Mansh, who did the research while he was a medical student at Stanford University in California.

Indoor tanning is linked each year to about 400,000 cases of skin cancer in the U.S., according to data cited by the Centers for Disease Control and Prevention.

The researchers write in JAMA Dermatology that previous studies suggested higher rates of indoor tanning and skin cancer among sexual minority men, but research was lacking on actual rates.

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For the study, the researchers used data from a 2013 national health survey and a survey from California conducted in 2001, 2003, 2005 and 2009.

The combined data included responses from about 78,000 heterosexual men, about 108,000 heterosexual women, about 3,100 gay and bisexual men and about 3,000 lesbian and bisexual women.

Based on the data, the researchers found the prevalence of skin cancer among gay and bisexual men ranged from about 4 to 7 percent, compared to about 3 percent among heterosexual men.

Gay and bisexual men were also between three and six times more likely to report indoor tanning than heterosexual men, the researchers found.

They also found that lesbians and bisexual women were 43 to 46 percent as likely as heterosexual women to indoor tan. They also had 56 percent as many reported non-melanoma skin cancers, the most common types of skin cancer, as straight women.

The study can't say why indoor tanning and skin cancer rates differ by sexual orientation, said Mansh, who is now affiliated with the California Pacific Medical Center in San Francisco.

He also cautioned that there are unmeasured factors that may explain some of the results, including rates of outdoor tanning and history of skin cancer screenings.

"Before we devote resources to trying develop target intervention programs, we have to understand why this group is at risk for elevated indoor tanning use," said Aaron Blashill, who co-authored an editorial accompanying the new study.

A more general media campaign informing gay and bisexual men of their increased risk may be beneficial while that data is collected, said Blashill, of San Diego State University.

Dr. Eleni Linos, who is a co-author of the new study and affiliated with the University of California, San Francisco, also researched the possibility of using Google's advertising service to tell people about the dangers of indoor tanning and skin cancer.

In a separate paper published in the same journal, Linos and her colleagues report that they created three ads with information about skin cancer and tanning. The ads were shown about 236,000 times and clicked more than 2,000 times, although researchers can't say whether the ads actually stop people from tanning.