GO UNDERCOVER IN NEW SUN-BLOCK GARMENTS.

Byline: Deborah Blumenthal The New York Times

For years, people who worry about skin cancer have been covering themselves with sunscreen. Now, another tactic is gaining favor: special clothing that promises to cut down on harmful rays.

The clothing is made with tight-woven fabrics that physically and in some cases chemically block most of the sun's harmful rays.

Dermatologists are enthusiastic about blocking the sun with clothing.

``It works,'' said Dr. William Mitchell Sams Jr., president of the American Academy of Dermatology. ``It appears to be very effective in achieving what we'd like, and there's no question that a single layer of a T-shirt or a short-sleeve shirt does not protect very well.''

The rate of all types of skin cancers has doubled since 1980, making the need to avoid the sun greater than ever. Darrell S. Rigel, associate professor of dermatology at New York University Medical Center, says people should ``wear protective clothing, avoid the midday sun and regularly use sunscreen.''

Just wearing a simple 4-inch-brim hat regularly will reduce the skin-cancer risk by 40 percent, said Rigel. That is because so many skin cancers occur on the head and neck, with one-third of all skin cancers occurring on the nose.

While everyone can benefit from clothes and sunscreen of an SPF, or sun protection factor, of at least 15 on all exposed areas, some people need to be particularly cautious, Sams said. These include anyone with a history of skin cancer, lupus or porphyria and those taking medications that increase sun sensitivity, such as certain diuretics, some antibiotics, some drugs for hypertension, ibuprofen and Retin-A.

While every clothing fabric acts as a sun barrier to some degree, studies show that the average cotton T-shirt offers an SPF of only 6 to 9. Rigel said this drops to an SPF of only about 3 if the shirt gets wet. SPF is a gauge of how a product prevents redness. Wearing a product with an SPF of 15 means it would take 15 times longer than unprotected skin to turn red.

Generally there is more protection with thicker fabrics, tighter weaves and darker colors. Though we feel cooler in light-color clothes, dark clothes absorb more ultraviolet light and protect the skin better. Wet fabrics are less protective than dry ones.

The new sun-protection clothes are lighter, cooler and more comfortable to wear than ordinary garments, which would have to be as thick as heavy wool, weighty cotton duck or even leather to offer equivalent protection.

Sun Precautions Inc. of Everett, Wash., which makes a line of SPF 30-plus clothing called Solumbra, was one of the first on the market, in 1992. It maintains that its clothes block out 97 percent of the sun's ultraviolet light, even after having been laundered 100 times.

Shaun Hughes, president of Sun Precautions, is a survivor of skin cancer. At 26, he found out he had malignant melanoma. The growth was discovered at an early stage and successfully removed. ``After that,'' he said, ``I became very concerned about sun protection and used to find that I'd sunburn right through normal clothes.''

His Solumbra line, available through a mail-order catalog, [phone], is marketed for the particularly sun-sensitive and includes hats, scarves, gloves, shirts, parasols, jackets, pants and skirts, ranging from $23 for a child's hat to about $85 for a man's long-sleeve water shirt.

Solumbra's effectiveness, Hughes said, is due to a combination of the fibers, weaving, dyeing and finishing of the nylon-based fabric. It contains no coating to make the fabric more sun-protective, he said.

Solar Protective Factory of Sacramento makes sun-protection clothing said to block 99 percent of ultraviolet B rays, and at least 90 percent of all ultraviolet rays, even after extensive wear-and-tear tests, as well as 40 launderings, the equivalent of two years of use.

There are two types of ultraviolet light that the manufacturers concern themselves with. Ultraviolet B rays are most directly responsible for burning. Ultraviolet A are slow-tanning rays, which penetrate deeper into the skin, age the skin and intensify the damaging effects of ultraviolet B.

The Koala Konnection's swimwear and activewear have been on the market for seven years in Australia, the country with the dubious distinction of having the area with the world's highest rate of melanoma, Queensland, in northern Australia.

For the last year, the line has been available through the company's United States division, based in Mountain View, Calif. It includes brightly colored children's clothing made of a patented fabric called HT2000, which mimics the look and feel of Lycra and is more durable, the company maintains, against the effects of chlorine and salt water.

The HT2000 fabric boasts an SPF of 100-plus, based on studies in Australia. Laundering tests have not yet been done in this country, but a company spokesman said the clothing should last at least two years. Sunsuits sell for $49. A line of sun-protection clothes for adults will be available in the United States in November. Koala Konnection clothes are sold at Zitomer Pharmacy in Manhattan, 969 Madison Ave., or by calling [phone].