it can help dry up acne, heal scars, relieve aching joints and produce vitamin D. But overexposure can also result in a variety of health hazards including skin cancer, cataracts and wrinkles.

Sunscreens can help protect your skin from the sun's harmful rays. The active ingredients in them are, in order of their effectiveness: p-aminobenzoic acid, or PABA; benezophenone derivatives; and PABA derivatives like glyceryl and isoamyl. Don't use a product that does not contain at least one of these ingredients.

The best way to choose a product is by its sun protection factor, or SPF. First, determine your skin type. Then buy a product in the range (they're numbered 2 to 20) that is right for you. Skin Type I people are very fair, tend to burn after 10 to 15 minutes of exposure, and never tan. Use No. 15 on your body and the highest factor you can find on your face. (Products with factors above 15 are harder to find; Clinique makes a good non-oily one for the face). Skin Type II people burn after 20 to 30 minutes in the sun. If they acquire a faint tan, it's after slow and gradual exposure to the sun. Use No. 15 to No. 20 on your face, even if you think you've primed your skin for the sun. Use No. 15 on your body during the first days out, then go no lower than No. 10. Skin Type III people usually burn after 30 minutes in the sun but eventually acquire a fairly dark, even tan. Use No. 10 to No. 12 on your face and don't drop lower than No. 7 or No. 8 on your body. Skin Type IV people almost never burn. Their skin is naturally dark or black, and exposure to the sun quickly makes it darker. A No. 7 or No. 8 should provide adequate protection for your face during your first days out in the sun. Always use some kind of protection on both your face and body. Even black people can severely dry out their skin, and in rare cases develop skin cancer, if they spend time in the sun unprotected.

To determine how long you can stay in the sun without burning while you are wearing a sunscreen, multiply the number of minutes it takes your unprotected skin to burn by the SPF number. For example, a Type II person who burns in 10 minutes can be in the sun 15 times longer, or about 2 1/2 hours, when protected by an SPF 15 product. But remember that other factors may speed your sunburn, such as the more direct rays of the tropical sun, or the rays reflected off sand or snow.

One drawback to the SPF system is that people mistakenly believe that if they use the products diligently, they are immune to sun damage. The best protection is to avoid sunbathing.