ATLANTA (AP) -- Half of U.S. adults under 30 say they have had a sunburn at least once in the past year, a government survey found -- a sign young people aren't heeding the warnings about skin cancer.

The rate of sunburn is about the same as it was 10 years earlier, reversing progress reported just five years ago.

"I don't know that we're making any headway," said Dr. Len Lichtenfeld, the American Cancer Society's deputy chief medical officer.

Experts say that even one blistering burn can double the risk of developing melanoma, an often lethal form of skin cancer.

The Centers for Disease Control and Prevention released the study Thursday, which was based on a 2010 survey of about 5,000 U.S. adults ages 18 to 29. The study showed that the share of those who said they had had a sunburn in the preceding year went from about 51 percent in 2000 to 45 percent in 2005, but then went back up to 50 percent in 2010.

Researchers don't know for sure why the sunburn rate picked up again, said Dr. Marcus Plescia, director of the CDC's Division of Cancer Prevention and Control.

Surprisingly, the CDC also found an increase since 2005 in how many people said they wear sunscreen or take other steps to protect their skin. But only about a third said they usually wore sunscreen. And the increasing rate of sunburns suggests many people are not putting on enough or re-applying it sufficiently, some experts said.

Also on Thursday, the CDC released findings from the survey on how many people use tanning beds, booths or sun lamps, and Lichtenfeld said of the results: "I am astounded."

About 6 percent of all adults said they had done indoor tanning in the previous year. The rates were much, much higher in young white women: About 32 percent of white women ages 18 to 21 had done indoor tanning, and nearly as many white women 22 to 25 did.

A similar survey in 2005 found about 27 percent of young women said they had done indoor tanning.

The latest study found indoor tanning often involved more than one trip to a salon for the novelty of it, or to bronze for a special occasion. Women in their 20s said they did indoor tanning more than 20 times in the previous year, on average.

Another surprise: As many as 13 percent of women who had a family history of skin cancer had done indoor tanning.

Experts said there is no longer significant scientific debate that indoor tanning causes cancer. In 2009, tanning devices were classified as carcinogenic by the World Health Organization. That was based on an analysis of 20 studies that found the risk of melanoma rose 75 percent in people who started indoor tanning before age 30.

"It's not a question of whether tanning beds cause cancer anymore. We've been able to prove that," said Dr. Jerry Brewer, a Mayo Clinic dermatologist and researcher.

And there does seem to be more public understanding of the risks. Witness the public revulsion last month over the case of a deeply bronzed New Jersey woman arrested for allegedly taking her 5-year-old daughter into a tanning booth. Police said the kindergartner suffered a burn. (The mother denied taking her into the booth and said the girl got sunburned from being outdoors.)

Morgan Weese, a 23-year-old Arizona woman tanning at Miami Beach in Florida, said she used to work at a tanning salon and uses the tanning beds three times a week before summer. "I just make sure that I am being safe about it, doing it in moderation. I'm not looking orange and I'm not going overboard," she said.

Indoor tanning took off about 30 years ago. There are nearly 22,000 salons across the U.S., serving an estimated 28 million customers, according to IBISWorld, an industry research firm.

Melanoma rates have been increasing for at least three decades. About 76,000 cases will be diagnosed in U.S. adults this year, and about 9,200 people are expected to die of the disease, according to the cancer society.

The CDC's Plescia said tanning beds are driving "an epidemic in the making."

Others shared that concern.

"It's the sunburn you got when you were 18 that leads to the cancer you get when you're 40. That sunburn will come back to haunt you," warned Dr. Zoe Draelos, vice president of the American Academy of Dermatology.

Danielle Itgen, 22, said skin cancer runs in her family but she still likes to sunbathe in the summer - while wearing sunscreen. "I feel like when I'm really pale, I look sick," she said during a visit to Miami Beach.

Elizabeth Garrido, 40, used to sunbathe every day when she was younger and still goes to the beach twice a week to soak up the rays.

Does she worry about skin cancer?

"Not at all," the Miami Beach resident said. "What's going to happen is going to happen. ... Besides, I like the beach. It's therapeutical."

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