Beverly Hills dermatologist Arnold Klein may be skin doctor to the stars, but now that the season for Doonesbury's "George Hamilton Cocoa Butter Open" is here, it's the sun that is on Klein's mind. With good reason. "Skin cancer is the most prevalent type of cancer," warns Klein, "and its principal cause is the ultraviolet rays in sunlight." With a 90 percent cure rate, skin cancer is the most treatable form of the disease. But one type—malignant melanoma (cancer of the skin's pigment-making cells)—is particularly virulent and can be fatal. It often begins with changes in the shape of a mole (the borders become notched) or its color—to hues of brown as well as black, white, blue and red. Early detection leads to a high cure rate.

While Klein says the best way to avoid these problems is simply to stay out of the sun, sunscreens are the second-best solution. The most widely used contain PABA (para-aminobenzoic acid), a colorless, odorless substance that absorbs ultraviolet B rays, the sunburning part of the spectrum. For those allergic to PABA, there are sunblocks on the market without it.

Just how much caution is called for and how strong a sunscreen is needed (it is sold in grades: No. 15 provides maximum protection) depends on skin type: Type I burns easily and never tans, Type II burns easily and tans minimally, Type III burns moderately and tans gradually and Type IV tans readily. "Anyone can develop skin cancer," Klein says, "but it most often occurs in Types I and II people who get too much sun."

That is not to say that shade or clouds prevent burning, since the damaging rays penetrate clouds and can be reflected off sand, sidewalks and snow. Perhaps the biggest myth of all, says Klein, is that suntan lotion promotes tanning. "Skin will tan according to type," he insists, "regardless of what you use." (Women who are pregnant, on the pill or taking other estrogenrelated drugs may be photosensitive whatever their skin type, and should also avoid overexposure.)

As for indoor tanning products, Klein says, "They contain dihydroxyacetone, a colorless substance that reacts with the skin to form a yellow-brown-orange hue that may last for weeks, but provides little protection against sunburn." Klein also decries sunlamps ("People abuse them") and tanning parlors ("My endorsing them would be like the lung association condoning smoking").

For those who do get sunburned, Klein suggests taking aspirin immediately to inhibit swelling ("Don't wait until you're in pain, it'll be too late"). Once the sting begins, use emollient lotions and compresses, then corticosteroid creams and sprays like Cortaid and Dermolate if it worsens. Home remedies such as baths in tea or baking soda may, contends Klein, "reduce discomfort. But they won't prevent swelling, blistering or peeling."

Klein, the son of an Orthodox rabbi in Mount Clemens, Mich., has been painfully aware of skin problems since age 2½, when he accidentally plunged his arm into scalding water and suffered severe burns that required six months' treatment.

He graduated from the University of Pennsylvania School of Medicine in 1971, moved to L.A. and went into private practice with another doctor—only to quit after two months. "I didn't like treating pimples and blackheads," he explains.

A rich aunt convinced Klein to set up practice in Beverly Hills instead. "I went from door to door like a Fuller Brush salesman," he recalls, "saying to every physician, 'Look, I'm really good, so send me your most difficult cases.' Six months later I had a full practice." One of his patients, Merv Griffin, was so impressed with Klein he invited him on his show—a stint the doctor has repeated several times.

A 36-year-old bachelor, Klein now lives in a $2 million 30-room Hancock Park mansion. "I feel guilty living here," he says. "I have it too good." He shares the space with his brother Steve, two aunts, one cousin, a cook and a housekeeper with a child.

Klein is co-author, with L.A. Dr. James Sternberg, of The Skin Book (Macmillan, $9.95), now in its third printing and due out in paperback this fall. He also plans on collaborating with Alex Haley's lady, My Lewis, on a book about black skin care. Blacks, he points out, seldom get melanoma (except on hands and feet) and require up to 15 times the ultraviolet rays to get as badly sunburned as whites. Regardless of race, Klein's message is the same: "Your skin never forgets the sun. If you want to look 20 years younger 20 years from now, stay out of it."