Teen-agers and young adults increasingly are being diagnosed with skin cancer, according to doctors who warn that the development could herald a wave of deadly lesions later in these patients' lives.

This onset is much earlier than in previous generations: Malignancies once thought to take 20 to 30 years to become noticeable are being removed from the faces, backs and necks of what one dermatologist described as "remarkably young" patients.

Melanoma -- the deadliest form of skin cancer -- now ranks as the most common cancer among people age 25 to 29. From the mid-1970s to the late 1990s, melanoma rates rose 60.5 percent among women age 15 to 29, according to figures from the American Cancer Society. That translates into 6.9 melanomas for every 100,000 women in that age group.

Among men in the same age group, the rate rose 26.7 percent in that period, to 3.8 for every 100,000.

While melanoma statistics can be tracked because doctors report cases to central cancer databanks, there's no comparable tally of more common skin malignancies such as basal cell and squamous cell carcinomas, or of a pre-cancerous condition called actinic keratoses. But estimates from the American Cancer Society suggest rates of the skin carcinomas are also on the rise. No one disputes that skin cancer rates overall remain highest in the elderly, in whom tumors have had a lifetime to develop.

But doctors are especially disturbed by the numbers of younger people they're treating, which suggest that messages about sun avoidance still aren't getting through and that the tan made popular by French designer Coco Chanel in the 1920s remains a sought-after look today.

Although doctors lack the data to know what exactly is behind the rise in skin cancers among young people, they suggest that several factors -- more time in the sun, improper use of sunscreens and a rise in tanning salon visits -- all play roles.

In a study published in 1997 in the Journal of the American Academy of Dermatology, a research team led by Dr. June K. Robinson at Northwestern University Medical School found that during the decade ending in 1996, the number of Americans who reported at least one severe sunburn rose from 30 percent to 39 percent.

Bad sunburns, especially early in life, are one of the best-established risk factors for melanoma, along with fair skin and multiple moles.

And more Amer-icans -- roughly 1 million a day -- are visiting tanning salons, according to the American Aca-demy of Dermatol-ogy. The Indoor Tanning Associa-tion, a trade group based in Jackson, Mich., estimates that 28 million Americans visit a salon at least once a year. Numerous studies over the years have linked the use of tanning beds to melanoma.

Doctors also say that advances in sunscreen technology, while helping protect people from sun exposure, have an unintended consequence: People feel protected when they slather on sunscreens with an SPF of 45 or higher to avoid the blistering burns linked to melanoma. But this may produce a false sense of security because people think the added protection enables them to stay in the sun longer, so they absorb more radiation.

David J. Leffell, a Yale University dermatologist, said the prospect that today's young skin cancer patients could develop more invasive cancers decades from now "represents a major public health problem."

We get 85 percent of our lifetime sun exposure by age 18, during a time when skin cells in our growing bodies are particularly vulnerable to damage. Ultraviolet radiation begins penetrating the skin "the first time your mommy puts you in a stroller for a walk," Leffell said.

Jane E. Allen is a reporter for the Los Angeles Times, a Tribune Publishing newspaper.

Facts about sunscreens

We've all heard that to protect our skin from the sun's aging effects and cancer-causing rays, we should stay out of the sun. The next best thing is to apply sunscreen or wear protective clothing.

One thing that some people don't realize is that there are two types of ultraviolet radiation that can age your skin and lead to cancer, and the SPF ratings on most sunscreens address only one: the potent burning rays, or UVB.

The higher the SPF rating on your sunscreen, the more short-wave radiation, or UVB rays, it's keeping from your skin.

Increasingly, though, dermatologists are concerned about the role of long-wave ultraviolet radiation, known as UVA radiation. These are the rays that penetrate below the epidermis of the skin, into the dermis, where the body makes collagen and elastin that provide skin's firmness and structure.

There is no rating system in place to quantify how well sunscreens shield us from UVA radiation, which is the main type that people are exposed to at tanning salons as well as through sun exposure; solar radiation is about 95 percent UVA and 5 percent UVB.

The American Academy of Dermatology has asked the Food and Drug Administra-tion to establish labeling standards for UVA sunscreen ingredients similar to the SPF rating used for UVB.

For now, it's up to consumers to find adequate products:

* Many products that block UVA rays contain physical sunscreens that reflect, scatter or absorb light. They include zinc oxide, the pasty white cream, and another heavy cream called titanium dioxide.

You might recognize on some labels the term "micronized zinc oxide," which refers to a lighter version of zinc oxide. There's also a newer chemical sunscreen, Parsol 1789, that absorbs UVA light.

The jury is out on how well any of these products protect from UVA rays.

* Dr. Arnold Klein, a California dermatologist, recommends mexoryl, a product derived from camphor that's available in sunscreens in Europe but not yet in the United States.

Mexoryl has been shown in European studies to offer superior protection against a broad range of UVA radiation. It's available in the Anthelios sunscreen line made by France's La Roche-Posay.

The FDA is reviewing mexoryl for sunscreen use. For now, you can buy Anthelios products in Canada or France, or from foreign-based Internet sites.

* Dermatologists say sunscreens are applied too sparingly.

They recommend that people apply sunscreens with a rating of at least SPF 15 as part of their daily ritual, before going out of doors. When outdoors, sunscreens should be reapplied after 30 minutes in the sun and every couple of hours after that.

-- Los Angeles Times