TEQUESTA, Fla. – On their way home from an SAT tutoring session, the Van Dresser twins, Alexandra and Samantha, 17, popped into Tan Fever & Spa, a small family-owned salon tucked into a strip mall between a bar and a supermarket.

They wanted to get tan before the prom, and the salon was the perfect combination of fast and cheap: Twenty minutes in a tanning bed cost just $7.

“It’s the quickness of the tanning bed,” Alexandra explained one afternoon last year. “We don’t have time to lay out on a beach.”

Indoor tanning might seem like a fashion that faded with the ‘80s, but it remains a persistent part of American adolescence, popular spring, summer and fall but especially in winter, when bodies are palest. Salons with names like Eternal Summer and Tan City dot strip malls across the country, promising prettiness and, in some cases, better health, despite a growing body of evidence that links indoor tanning to skin cancer.

Here in the Sunshine State, there are more tanning salons than McDonald’s restaurants, CVS stores or Bank of America branches, according to a 2014 study by University of Miami researchers.

For decades, researchers saw indoor tanning as little more than a curiosity. But a review of the scientific evidence published last year estimated that tanning beds account for as many as 400,000 cases of skin cancer in the United States each year, including 6,000 cases of melanoma, the deadliest form.

And clinicians are concerned about the incidence rate of melanoma in women younger than 40, which has risen by a third since the early 1990s, according to data from the National Cancer Institute. (Death rates have not gone up, however, a testament to earlier detection and better treatment.)

“We’re seeing younger and younger patients coming to us with skin cancer,” said Dr. Eleni Linos, assistant professor of dermatology at the University of California, San Francisco. “That is a new phenomenon.”

As such worrying signs have accumulated, tanning has emerged as a serious public health concern. Last year, the surgeon general called on Americans to reduce their exposure to the sun and tanning beds to prevent skin cancer, and the Food and Drug Administration invoked its most serious risk warning, lifting tanning beds from a category that included Band-Aids to that of potentially harmful medical devices. The Obama administration’s 2010 health care law imposed a little-noticed 10 percent tax on tanning salons.

And more than 40 states now have some sort of restriction on the use of tanning salons by minors, according to AIM at Melanoma, an advocacy and research group based in California, the first state to adopt a ban on minors in 2011. At least nine states plus the District of Columbia (pending congressional approval) have passed such bans, even Republican-controlled Texas, where antipathy to government regulation runs deep.

“The tide is turning,” said Samantha Guild, director of public policy at AIM. “States are saying: ‘We don’t have to go out on a limb on our own. There’s broad support for this issue.’”

For the first time, new federal data has documented a decline in the use of indoor tanning among teenage girls, dropping to about a fifth of them in 2013, from a quarter in 2009. Gery P. Guy Jr., a researcher with the Centers for Disease Control and Prevention who analyzed the data, which was released in December, attributed the decline to greater awareness and tougher laws.

Even so, public health experts say tanning remains a persistent problem, especially among white teenage girls, a full third of whom say they have tanned indoors, more than the share who smoke cigarettes.

There were about 14,000 salons across the country as of early 2014, according to John Overstreet, executive director of the Indoor Tanning Association. That does not count tanning beds in gyms and beauty parlors. The number is down about a fifth in recent years, he said, as the recession eroded young women’s disposable income and the tax imposed under the new health care law squeezed salons’ profits.

Overstreet argues that there is no science that conclusively links moderate, nonburning ultraviolet ray exposure to melanoma. His organization’s mission, according to its website, is “to protect the freedom of individuals to acquire a suntan.”

“The folks who don’t like this industry are exaggerating the risks,” he said, adding: “It’s just like anything in life. If you get too much of it, it’s bad for you.”

A Cancer Link

Evidence of the link between melanoma and ultraviolet exposure may have been inconclusive a decade ago, but recent research, including fresh data from the Cancer Genome Atlas, a federally funded program that is cataloging genetic mutations responsible for cancer, bolsters the case for the link.

Dr. Jeffrey E. Gershenwald, a leader of the melanoma Atlas project, said studies to date showed that a majority of melanomas initially arising on the skin contain mutations associated with ultraviolet exposure. As for burning, one recent study controlled for that, and still found an increased risk from indoor tanning.

“There’s no longer a question of whether UV is important,” said Gershenwald, medical director of the Melanoma and Skin Center at the University of Texas MD Anderson Cancer Center. “Genomics has been transformative in our understanding of melanoma.”

The problem with indoor tanning, researchers say, is that many of those who do it, do it a lot. The federal government has collected data on tanning among high school students only since 2009, but researchers were surprised at the findings: Among those who used tanning beds, more than half had used them 10 times or more in the past year, according to Guy.

Alan Geller, a senior lecturer at the Harvard School of Public Health, said, “We’ve been astounded by how many young people are using tanning beds and how often they are using them.”

Heather Champion, who manages a beauty salon in Palm Beach, Florida, said she had tanned so often in high school in upstate New York that her tanning card, which listed her visits, often needed additional pages, like a world traveler’s passport.

“There were some days I would go twice,” she said.

Four years ago, at age 26, she learned she had melanoma. The doctors caught it early and removed the cancer, but she still has to monitor her skin. Now she looks at herself in family pictures from those years and cringes.

“I was so much tanner than everyone else. It’s just weird,” she said.

There is strong peer pressure to be tan, particularly in small-town high schools.

Sarah Hughes started tanning at 16, during beauty pageant season in her hometown, Dothan, Alabama. She often tanned five days a week, paying with money earned working at Pier 1 Imports. In her senior year, she got a job at a tanning salon so she could tan for free.

“Living in a small town in southern Alabama, you don’t want to be the oddball out,” said Hughes, who is now 30 and works as a loan processor in a bank.

Over time, she came to crave it.

“People did drugs. People had eating disorders. I tanned,” she said.

Joel Hillhouse, director of the Skin Cancer Prevention Laboratory at East Tennessee State University, said such compulsive behavior is not uncommon. A small share in a survey he conducted even admitted to stealing money and breaking into tanning salons to tan.

Hughes stopped tanning at 25 when a doctor diagnosed advanced melanoma. A tumor on her left leg had grown down into her muscle and, eventually, her lymph nodes. In all, she had 33 spots removed, including eight melanomas over two years, a searing experience.

She survived.

Brandi Dickey, from Fort Worth, Texas, did not. Her mother, Paula Pittsinger, blames the near constant tanning from the age of 14 to 28, when she was found to have a particularly aggressive form of cancer that eventually spread throughout her body to her brain. She died in October at 33 after 18 surgical procedures, including six on her brain. There was no history of melanoma in her family.

“When you see the impact, the brain surgeries, the scars, when you see what tanning has done, it has got to hit home that it’s just not worth it,” Pittsinger said.

When Pale Became Passé

It was not always desirable to be tan. For generations, parasols and the pale skin they protected were signs of upper-class privilege. Being tan was like having calluses – something associated with working-class people who toiled in jobs that exposed them to the sun, according to “Suntanning in 20th Century America,” a social history of tanning by Kerry Segrave, published in 2005.

But in the early 1900s, the medical profession began to promote the health benefits of tanning. Workers were increasingly moving into factories where complexions grew pallid, as the upper classes spent more time outside playing sports. By the 1920s, a tan had become fashionable, surfacing in conversations among affluent society types in F. Scott Fitzgerald novels. A character, Maury Noble, mused in “The Beautiful and Damned,” published in 1922: “I did use to get a pretty good tan. I used to get a sort of bronze, if I remember rightly.”

“The 1929 girl must be tanned,” an article in Vogue proclaimed, Segrave reported.

Indoor tanning exploded in popularity in the United States in the 1980s and 1990s.

Dr. June K. Robinson, a professor of dermatology at Northwestern University’s Feinberg School of Medicine, remembers being handed a bright orange flier for free tans in downtown Chicago in the early 1980s.

“I’m waiting for the light to change, and I’m saying to myself this is the stupidest thing I’ve ever heard of,” she said.

Many factors, including genetics, are at play with skin cancer. But exposure to ultraviolet light causes a majority of cases, and scientists have been trying to gauge how big a role indoor tanning plays. A panel of experts convened by the World Health Organization found in 2009 that the use of sun beds before age 30 was associated with a 75 percent increase in the risk of melanoma. A 2012 study found a 15 percent increase in the risk of certain skin cancers with every four sessions in a tanning bed before age 35.

Overstreet contends that more people may be finding melanomas because more people are going to the doctor to look for them.

Experts say the increase is real, and not just a matter of better detection. Thicker, more dangerous tumors are rising just as fast – particularly among young women – and rates are also up among the uninsured, who would be less likely to get medical checkups.

A Craving for Confidence

Many young women said in interviews that tanning fed a craving to be pretty, at a time in life when it is most acute. Madison, 21, a student at the University of Rhode Island, said tanning made her feel “more confident and more comfortable when I walk around.”

“Sometimes it makes me feel thinner,” she continued. “It has all these weird effects that just make me feel better about myself.”

She recently reduced her use to a few times a month, down from almost daily, honoring a request from her mother.

“I’d love to stop tanning, but I can’t,” said Madison, who asked that her last name not be used because she felt self-conscious about the issue. “Confidence is such a touchy aspect of a girl’s life. It takes a lot of time and practice. I’m just not there yet.”

The CDC’s national youth survey found that indoor tanning often goes along with binge drinking and unhealthy weight-control practices. Among teenage girls, it was associated with illegal drug use and having sex with four or more partners, and among boys with the use of steroids, daily cigarette smoking and attempted suicide. Boys also tan indoors, but their numbers are a small fraction of the total.

Some experts say combating the problem is a matter of raising awareness about the dangers of tanning. But many women said in interviews that they were aware of health risks but cared more about how they looked now.

“If I get skin cancer I’ll deal with it then,” said Elizabeth LaBak, 22, a student at Westfield State University in Massachusetts. “I can’t think about that now. I’m going to die of something.”

The Van Dresser twins in Florida say they slather their moles with sunscreen before they get in a tanning bed. They even joined a melanoma awareness club in their high school. But the pressure to be tan is strong, and they find it hard to resist.

“It’s what teens do,” Samantha said. “Especially in Florida.”

The new state laws restricting tanning by teenagers seem to be having some effect. According to Guy, the CDC researcher, female students in states that require a combination of parental permission or other age restrictions are 40 percent less likely to tan indoors.

LaBak said fewer women on campus tan now.

“All the Victoria Secret models are pale now,” she said.

Even so, salons persist. About half the country’s top 125 colleges have tanning beds on campus or in off-campus housing, University of Massachusetts medical school researchers reported in October. But LaBak’s favorite spot, Beach Club Tanning, a salon in a strip mall next to a CVS and a Big Y grocery store that offered $2 tans, has closed, and “now there’s no place that’s cheap enough,” she said.

“The tanning thing is like the smoking thing,” she said. “Everyone used to smoke. And then they said, ‘You’ll die of lung cancer.’ That’s what’s happening to tanning.”