CHICAGO -- The rising rate of skin cancer has researchers working to determine what's causing it. But a new report leaves more questions than answers, researchers say.

British researchers reviewed all the major studies on tanning beds to see if the activity increases malignant melanoma -- the most serious, often fatal, form of skin cancer.

Six studies found that tanning beds increased the risk of melanoma. Five studies found they did not. But the most recent study found a huge connection, the researchers said.

"I don't think anybody can say what causes skin cancer to date," said Dr. Candace Thrash at Chicago's Swedish Covenant Hospital. "We know [ultraviolet] radiation does cause skin cancers."

Thrash said tanning beds emit two kinds of ultraviolet light -- UVA and UVB. UVA causes aging, and UVB causes sunburns. Thrash said tanning beds emit mostly UVA light.

UVA was thought to be the safer kind -- but not according to the latest study.

"We think the UVA rays can cause skin cancer, as well," Thrash said. "So there really is no such thing as a safe tan. You know, at best you're going to end up with aging of your skin after using a tanning bed. And, at worst, you could end up with skin cancer."

Doctors said there's also a whole generation of adults born before tanning beds who are at risk for skin cancers. They got bad sunburns as children -- no one talked about sunscreen then.

"I spent a lot of time at the beach with baby oil, iodine -- doing everything you could possibly do to damage your skin," said patient Ann Cunniff.

Thrash examined Cunniff's skin for unusual-looking moles that could indicate skin cancer.

"I had a couple of suspicous moles. I thought I better get them checked out," Cunniff said.

One under her arm was removed for testing to see if it's cancerous. Thrash recommends that anyone at risk for skin cancer get a mole-and-skin exam every year.