Atlanta ? State laws meant to keep teens out of indoor tanning booths haven’t made a dent, a new study has found, disappointing doctors hoping to reduce deadly skin cancers. The researchers say it’s not clear why the laws failed, but pointed to lax enforcement as a factor.

The study is the first to look at the laws’ impact. Some medical experts were disturbed by the findings, saying more needs to be done about the health threat from indoor tanning parlors.

“Basically, these are businesses that are exposing teenagers to carcinogens,” said Dr. Jeffrey Sosman, a melanoma researcher at Vanderbilt University who was not involved in the study. Mela-noma is the deadliest form of skin cancer and has been linked to childhood sunburns.

An estimated 30 million Americans are customers of the nation’s 25,000 indoor tanning businesses, according to the Indoor Tanning Association. The organization argues that indoor tanning, when done properly, can improve health.

Tanning parlors are popular with girls and young women; as many as one in three use indoor tanning, some studies suggest.

U.S. cases of melanoma have been increasing. It’s not clear to what extent indoor tanning has played a role in that trend, but people who start indoor tanning when they’re young have a higher risk of melanoma, scientists say. Melanoma can almost always be cured if caught early.

About 20 states now have some law aimed at curbing minors’ use of indoor tanning, said Vilma Cokkinides, an American Cancer Society researcher who was one of the study’s authors. Kansas is not among the states.