(MONEY Magazine) – If your mother didn't tell you, pop radio will: You should use sunscreen. The surprise is that most of us don't. In a 1998 survey by the American Academy of Dermatology, only 15% of respondents used sunscreen whenever they went outside, as doctors recommend; only four in 10 thought protection from the sun was very important. Meanwhile, over the past two decades new cases of malignant melanoma, the deadliest form of skin cancer, have doubled, and the cost of treating new skin cancer cases is expected to exceed $563 million in 1999. Nearly 10,000 people will die of skin cancer this year.

In an effort to help consumers, the FDA introduced new labeling regulations for sunscreen and tanning products on May 20. By 2001, manufacturers will have to eliminate the terms "sunblock" and "waterproof" from labels. (No product completely blocks harmful rays or is completely waterproof. "Water resistant" and "very water resistant" are the new terms.) Within 12 months, manufacturers will have to place warnings on tanning products that have no sunscreens, stating that they do not protect against sunburn or skin cancer. And high-protection products that boast SPFs over 30 will be permitted to state only that they are SPF 30+.

In the meantime, how should you choose a sunscreen that protects you?

KNOW HOW THE SUN HARMS SKIN

The villain is ultraviolet radiation--UVA, UVB and UVC. UVA, which is emitted by tanning machines as well as the sun, was once believed to be harmless. Recently, however, UVA has been implicated in the development of cancers. UVB radiation damages DNA, which triggers abnormal skin-cell growth, causing wrinkling, burning and cancers. (Sun damage shows up as freckling, raised moles, spider veins or uneven pigmentation long before cancers develop.) UVC, which is known to be toxic, is mostly filtered out in the earth's upper atmosphere by the ozone layer.

GET BROAD-SPECTRUM PROTECTION

Since the FDA doesn't set a standard for UVA protection, Maria Polikandritou Lambros, a sunscreen expert at the University of Oklahoma College of Pharmacy, recommends that you choose a sunscreen that contains zinc oxide or avobenzone (also called Parsol 1789). Look on the label for the words broad spectrum.

Greasepaint-like physical sunblocks such as zinc oxide (also found in diaper rash ointment) and titanium dioxide reflect and scatter UV radiation. They provide the broadest protection and are especially good for people with sensitive skin. And forget the thick white gunk you used to see on lifeguards--new methods of processing these compounds into microscopic particles have made them more cosmetically appealing.

Fourteen chemicals that absorb portions of UV radiation also have been approved for use as sunscreens by the FDA. They fall into several broad categories: P-aminobenzoates, salicylates, cinnamates, benzophenones, dibenzoylmethanes and anthranilates.

The FDA does set standards for UVB protection. The sun protection factor (SPF), which is based on these standards, measures how long the product will allow you to stay in the sun without turning red. Let's say you normally begin burning in 20 minutes. If you apply an SPF 30 product every two hours or so, it should take about 600 minutes (10 hours) for enough UV to get through to burn your skin. (Reapplying sunscreen does not buy you additional time without burning.)

Dermatologists recommend sunscreens with an SPF of at least 15; fair-skinned people with light eyes and hair shouldn't use anything less than SPF 30. "A sunscreen of SPF 8 should be an oxymoron," says Mark Naylor, a dermatologist at the University of Oklahoma. If you'll be outdoors at a high altitude, in the tropics or around water or snow, get the highest SPF products you can find, he adds.

The sunscreen's form--whether it's lotion, oil, cream, oil-free (for the acne-prone) or spray-on--matters only to the extent that it's convenient enough for you to use faithfully. Lambros says that lotions stay on better and spread more uniformly than oils, but she also likes the new spray-on products. She recommends rubbing them into the skin for even coverage.

Apply sunscreen liberally (at least one ounce for your whole body) 20 minutes before leaving the house. Reapply every few hours--more often if you swim or perspire heavily. Most people don't use enough to get the optimum effect.

And bear in mind that sunscreen alone will not protect you completely. Its use prevents squamous cell and basal cell carcinomas, but the evidence is less conclusive for deadly melanomas. The prescription for fair-skinned people or those with a family history of skin cancer: "Hats, long sleeves and shade," says Marianne Berwick, Ph.D., an epidemiologist at Memorial Sloan-Kettering Cancer Center in New York City. Or stay inside.

E-mail your health questions to health_column@moneymail.com.