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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Associated Press writer Suzette Laboy in Miami contributed to this report.

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Online:

CDC reports: http://www.cdc.gov/mmwr

The response “dwarfs any past organ donation initiative,” said David Fleming, chief executive of Donate Life America, in a statement.

The Facebook feature allows users to share their decision to be an organ donor on the website. More than 100,000 did that by Tuesday night, according to Facebook, which is working with Fleming’s group to encourage Facebook users to also officially register as donors with their state.

A link on the site connects to online donor registries. At least 22,000 people had followed that link as of Wednesday afternoon. Information from 22 states indicates that a third or more of them filled out the form to register, said Donate Life America spokeswoman Aisha Michel.

California — where Facebook is headquartered — reported startling results. About 70 people register online as organ donors each day. But in the 24 hours after Zuckerberg’s announcement, about 3,900 signed up.

“We’re just thankful we have this opportunity to bring more people into the process,” said Bryan Stewart, a spokesman for OneLegacy, which coordinates transplants in the Los Angeles area.

“We’re looking forward to seeing how long this activity lasts, and at what level,” he added.

Facebook, a social network site founded in 2004, has 526 million daily users around the world. It was Facebook’s idea to add the option, after Zuckerberg took a personal interest in the issue, Michel said. The feature is available in the U.S. and the United Kingdom.

As with some personal information on Facebook, organ donor status can be kept private or shared publicly or only with friends.

More than 114,000 Americans are currently on waiting lists for transplants of kidneys, livers, hearts and other organs, according to United Network for Organ Sharing (UNOS), the organization that runs the nation’s transplant system. More than 6,600 died last year waiting for an organ.

According to UNOS, 43 percent of adults in the U.S. are registered as donors. Organs can only be used though under certain circumstances, such as when someone dies from a major head injury and a ventilator can keep the organs viable. Less than 1 percent of U.S. deaths annually are under such circumstances. And sometimes the opportunity is lost because family members didn’t know about the person’s wishes on organ donation.

The Facebook feature “is a unique opportunity for people to make their decision known,” UNOS Executive Director Walter Graham, said on a statement.

Most people register as organ donors when they get a driver’s licenses, but about 2 percent sign up through online registries. Both represent legal consent for adults. For children who want to be donors, parental consent is still required.

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Online:

Donate Life America: http://donatelife.net/

Facebook directions: http://tinyurl.com/794o4d9

“These were catastrophic winds that could destroy pretty much anything in its path,” Cindy Chiu, an epidemic intelligence service officer, said in reporting preliminary findings this month at a Centers for Disease Control and Prevention conference in Atlanta.

Unlike in other tornado outbreaks, the largest group of people who died were in single-family houses — not mobile homes — the CDC analysis found.

The April 27, 2011, outbreak involved 62 tornadoes that stretched along ground-hugging tracks that covered more than 1,000 miles. Fatalities were reported from central Alabama to far north Alabama.

While many who heard the warnings sought shelter, others took their chances and lost.

The American Red Cross shares disaster data with the CDC, including what was gathered in extensive interviews with families of the deceased.

Relatives of an 80-year-old woman from Lawrence County “notified her of impending storm — asked her to go to storm shelter next door. She refused, said if her time to go, she would.”

The wife of a 35-year-old man from Franklin County heard the warning on TV, according to another vignette provided by Chiu. “She and sons went to basement of neighbors. He stayed in the home,” the vignette states. “Tornado struck (at) 330pm and he was found 30 mins later near a tree. He was badly injured and died in the hospital.”

The CDC has been examining reports of 255 deaths, including a few for which no Alabama death certificate has been found yet. It’s possible a few people were injured in Alabama but died in hospitals in nearby states, Chiu said.

For 120 of those 255, the CDC determined whether the victims knew of the coming tornadoes ahead of time. And 105 were warned.

Of those, 70 took some kind of protective action, like covering themselves or going to what they thought was a safer location or room — including 45 who sought proper shelter, like a basement or interior room on the lowest floor possible. Nineteen were in bathrooms, 10 in basements, 10 in bedrooms and 10 in hallways and smaller numbers in other rooms.

The average age of those who died was 50, and a third of the deaths were people 65 and older, the CDC found.

Being elderly is considered one of the greatest risk factors for death and injury in a tornado. Older people may be less mobile and have more difficulty getting to shelter. They may be frail, and more likely to die from an injury that might not kill a healthier and younger person.