Gyms are places people go to get healthier. But nearly half the gyms in the US contain a potentially addictive carcinogen—tanning beds, report UConn researchers in the July 18 issue of JAMA Dermatology.

Exercise reduces the risk of every cancer except one—melanoma, the deadliest form of skin cancer. People who exercise heavily are at greater risk of skin cancer, and yet many gyms in the US have tanning beds. In other words, tanning beds in gyms are targeting people who are already at higher risk of skin cancer.

Exercise and tanning are both activities people use to improve their appearance; and people who tan in gyms tan more often—and more addictively—than other people who use tanning beds, according to a study run by UConn psychologist Sherry Pagoto.

Pagoto, a professor of allied health sciences at UConn as well as president of the Society of Behavioral Medicine, points out that “by pairing exercise with tanning beds, gyms send the message that tanning is part of a healthy lifestyle. It is not.”

Pagoto and her colleagues surveyed 636 people who had used a tanning bed at least once in their life. Of those people, 24% had tanned in a gym at least once. Those who reported tanning at a gym tended to be heavier tanners overall, and were more likely to fit a profile of addictive tanning, agreeing with statements such as “my urges to indoor tan keep getting stronger if I don’t indoor tan,” and “at times, I have used money intended for bills to pay for my tanning sessions.” The study also found that greater tanning was associated with more frequent exercise, which is especially concerning, because of the connection between heavy exercise and skin cancer risk.

“Exercise and tanning are both things people use to look better, which may be why we see a connection between these two behaviors, and why gyms are providing tanning beds to patrons,” Pagoto says.

Researchers don’t know why exercise is associated with an increased risk of skin cancer. But they do know that the majority of skin cancers are caused by exposure to ultraviolet light, which is what tanning beds produce. Ongoing, occasional use of tanning beds triples a person’s lifelong risk of melanoma, according to the Melanoma Research Foundation, and the incidence of skin cancer has been rising for 30 years in the US. About 91,000 people will be diagnosed with melanoma in 2018, and about 9,000 will die from it, according to the American Cancer Society.

“Indoor tanning is the same class of carcinogen as tobacco, radon, and arsenic,” says Pagoto. “Those are not things you’d want around you while you’re working out.”