Tanning salons are feeling burned.

Their industry has been besieged by investigations, tougher restrictions, and a hefty new tax, as critics ranging from the World Health Organization to municipal health departments decry indoor tanning as harmful.

Adding to the heat, a rigorous new study finds that indoor tanning raises the risk of malignant melanoma, the most dangerous skin cancer, by 75 percent.

"I think it's about time we began to focus on indoor tanning as a risk factor," said University of Minnesota epidemiologist DeAnn Lazovich, lead author of the study published Thursday by the American Association for Cancer Research in Philadelphia.

John Overstreet, executive director of the Indoor Tanning Association, countered: "When you look at the greatest risk factors identified in this study, tanning isn't even one of the top factors. The number of moles the subjects had, how fair their skin was, and the color of their hair were all stronger indicators of their risk of melanoma."

As often happens when a public health concern clashes with personal freedom, the furor over indoor tanning comes with confusing statistics, controversial claims, and changing beliefs.

Ultraviolet radiation, whether from the sun or from tanning lamps, increases the chance of developing melanoma and other skin cancers. However, in the 1980s, sunburn-causing ultraviolet B rays were believed to be the bad actors, while deep-penetrating ultraviolet A rays were considered benign.

UVA rays are now known to do the worst skin damage.

The new study, the first to distinguish between UVA and UVB exposure, found that tanning beds emitting mostly UVA - which were standard in the 1980s - quadrupled the risk of melanoma for this group.

How big is that risk to begin with? The study wasn't designed to look at individual risk. It compared 1,167 melanoma cases with 1,101 healthy people to assess the strength of risk factors.

But the American Cancer Society says that over a lifetime, the chance of melanoma is about 1 in 50 for whites, 1 in 200 for Hispanics, and 1 in 1,000 for blacks.

While that makes the disease far less prevalent than, say, colon cancer, melanoma is becoming increasingly common in some parts of the world. In the United States - where there were about 69,000 new diagnoses and 9,000 deaths last year - the percentage of people who develop melanoma has more than doubled in the last 30 years, according to the National Cancer Institute. Among women ages 20 to 29 - the core of the indoor tanning market - melanoma is now the second most common cancer, behind only breast cancer, according to the American Academy of Dermatology.

Some experts believe part of this increase is due to misdiagnosis. As doctors strive to err on the side of caution, they are identifying melanoma earlier, when it is most curable - and most difficult to distinguish from a nonmalignant growth.

Meenhard Herlyn, a molecular biologist and melanoma researcher at Wistar Institute in Philadelphia, said modern lifestyles had contributed to the increase.

"We city folk are indoors all week, then we go out and get overexposed. The intermittent, intense sun exposure is a major factor," he said, adding that sunscreens were an insufficient antidote.

Still, the boom in bronzing may also play a part. Over the last 30 years, the U.S. industry has grown to a $5 billion enterprise, with more than 40,000 salons, gyms, spas, and other businesses offering tanning, according to the trade magazine Looking Fit.

William James, a University of Pennsylvania dermatologist and president of the American Academy of Dermatology, said the link between indoor tanning and skin cancer is now well-established.

"Early studies showed trends," he said. "The latest ones are quite definitive."

Last year, a World Health Organization panel reviewed the existing research, 19 studies done over 25 years. The panel concluded that tanning devices were "carcinogenic to humans," even though the link to melanoma was clear only for people who started tanning before age 35; their risk increased by 75 percent.

Lois Vespe, 44, of Cherry Hill, who is light-complected despite her Italian heritage, figures she made more than 100 trips to salons in her early 20s. In January, a suspicious mole on her back turned out to be melanoma, fortunately at an early, curable stage.

"I would never have gone to the tanning salon if I knew the dangers," she said. "We had doctors who told us going to a tanning salon was safer than sunbathing."

The Indoor Tanning Association promoted that misconception, as well as others, in a 2008 advertising campaign. That prompted the Federal Trade Commission to bring charges. This month, the association agreed to stop the deceptive claims, and to add disclosures about risks in promotional material.

But statistics cited by public health organizations can also be misleading. As the tanning association points out on its website, a 75 percent increase in risk sounds like a lot - unless it's put in perspective: "Is it 75 percent greater than an already-high risk, or a tiny one? If you read the FDA's 'Indoor Tanning: The Risks of Ultraviolet Rays,' or a number of other documents from the WHO and skin cancer foundations, you won't find your actual risk."

You will if you go to www.cancer.gov/melanomarisktool/ and use the melanoma risk assessment tool designed by scientists at the National Cancer Institute and the University of Pennsylvania.

Turns out that even for a freckled fiftysomething redheaded female whose skin cannot tan, the estimated five-year risk of melanoma is only two-tenths of 1 percent. Boost that risk by 75 percent, it's still less than 1 percent.

Statistics aside, society seems to be looking down on getting brown:

In July, indoor tanning services will be slapped with a 10 percent federal tax. The American Academy of Dermatology successfully pushed to add the tax to the national health reform legislation.

The Food and Drug Administration is considering strengthening warning labels on tanning beds.

Numerous states and countries have restricted or banned indoor tanning for teenagers. Late last year, Brazil, where sun worship is an art form, went even further, completely outlawing the sale and use of tanning devices.