* Sunscreens labeled "15" or higher protect me against all the sun's rays?

* A tan may protect me against some sunburn, but not against all wrinkling or skin cancer?

* I can endanger my skin by using too little sunscreen or not applying it one-half hour before going out in the sun?

* Infants under six months probably should not be in the sun at all?

* Sunlight coming through a window can damage your skin?

Even if you are more careful than ever about going out in the sun nowadays, you may be surprised at the answers to the above questions. All of them are true.

While you may be used to warnings about limiting sun exposure and using sunscreens, researchers are becoming ever more cautious about how much sun is good for you. The following questions and answers may help you decide how much sun you should be exposed to and what precautions you can take to protect yourself and your family.

Although sunlight is essential for human life, daily exposure to the sun over a lifetime is a major cause of skin damage, including wrinkling and skin cancer. Many of the skin changes attributed to aging are in fact signs of sun-induced skin damage. Every year, more than 700,000 people in the United States get skin cancer. It is the most common form of cancer, with rates growing three to five percent annually. Left untreated, skin cancer can be life-threatening.

Any tan indicates skin damage. Although a tan may give you some protection against sunburning, it will not fully protect you against wrinkling or skin cancer. Some people are especially vulnerable to the effects of the sun, such as fair-skinned individuals who burn easily and tan poorly or not at all. Of those who do tan well, the deeper the color of the tan, the more extensive the skin damage.

Staying indoors is the best protection against getting sun-damaged skin. The hours between 10 a.m. and 3 p.m. are the worst times to be outside. To help reduce the risk of skin damage from sunlight, wear tight-weave clothing that covers the body, wear a hat, and use maximum protection sunscreens.

Most people benefit from sunscreens with high sun protection factor (SPF) numbers, such as 15 or greater. The SPF number gives you some idea how long you can remain in the sun before burning. If, for example, you would normally burn in 10 minutes without sunscreen, applying a 15 SPF sunscreen may provide you with about 150 minutes in the sun before burning. Swimming and perspiration, however, will reduce the actual SPF value for many sunscreens. Sunscreens with SPF numbers greater than 15 may benefit those who want to minimize their exposure to the sun, especially those who are fair-skinned, live in climates close to the equator or at high altitudes, work or play outdoors, or perspire heavily. Because skin irritations may result from various sunscreen ingredients, you may want to first test a product by applying a small amount to a limited area of your skin.

Unfortunately, even sunscreens with high SPF numbers offer you less than full protection. Sunlight exposes you to two kinds of ultraviolet light, called UVA and UVB. Both can cause skin damage, including wrinkling and skin cancer. Although virtually all sunscreens provide some level of protection against UVB rays, no product yet screens out all UVA rays. SPF sunscreen numbers only indicate the amount of time you can stay in the sun without burning. Even if you don't burn, the sun's rays still may be damaging your skin. No rating system yet exists for UVA. There is no way, then, to tell how much UVA protection you are getting. Some researchers estimate that the level of protection in many products advertising UVA protection, even those with high SPF numbers, is probably equivalent to an SPF 3 or 4. So, even if you use high SPF number sunscreens, you still are vulnerable to skin damage from the sun's UVA rays.

You will not get the full protection offered by the sunscreen unless you apply the recommended liberal amount on your skin. Unfortunately, many people use much less. A sunscreen with an SPF of 15 may give only half that protection if you don't use enough of it. If you are at the beach, for example, use about an ounce of sunscreen over your whole body for one application. That means you should plan to buy about one 8-ounce container or more of sunscreen per person for each week you are at the beach. If you frequently go swimming or perspire, use a waterproof product for the best protection. Apply the sunscreen before going outdoors and be sure to reapply it as needed -- after perspiring, swimming or toweling off. Otherwise, you are not getting the protection you need from the sun's rays.

Skin damage does not occur only on the beach or the ski slopes. Most people who are going to be out in the sun for more than 10 minutes would benefit from daily use of sunscreen on the parts of the body exposed to the sun. Even casual exposure to sunlight -- while driving a car, walking to the store, taking an outdoor lunch break -- contributes to the cumulative lifetime exposure that may lead to skin damage. Make sure you apply the sunscreen about one-half hour before going out in the sun to give your skin a chance to fully absorb it. If you're taking medications, ask your doctor or pharmacist if these medications will sensitize your skin to the sun and aggravate sunburn or rashes. Common drugs that may do this include: certain antibiotics; birth control pills; diuretics; antihistamines; and antidepressants.

Sunscreens contain a variety of ingredients. Although some sunscreens may provide more moisturizers, for example, those with identical SPF numbers give you equivalent sunburn protection from UVB rays. Because of the cost of buying sunscreen products year-round, you may want to shop for competitively-priced brands of sunscreen offering the level of protection you need.

Do not be misled by sunscreen products that claim they are sunblocks. Only opaque substances, such as zinc oxide or titanium dioxide, totally block the sunlight. These products are most practical to use on specific areas of the body most exposed to the sun, such as the nose or lips.

Parents should see that sunscreens of SPF 15 or greater are applied routinely when children go outdoors. Because sunscreens may irritate baby skin, and babies' developing eyes are particularly vulnerable to sunlight, experts recommend that infants less than six months old should be kept out of the sun altogether. Experts estimate that about 50 percent of an individual's sun exposure occurs by age 18. Some have suggested that schools, child care centers, and camps rearrange outdoor play times to minimize exposure to the midday sun.

Tanning devices, like natural sunlight, emit ultraviolet rays. These UVA or UVB rays, whether from artificial or natural sources, can cause skin damage.

Your doctor or dermatologist may have additional material on tanning and sunscreens. For a free brochure on Indoor Tanning,contact: Public Reference, Federal Trade Commission, Washington, DC 20580; 202-326-2222. TDD (202) 326-2502. For a list of all the FTC's consumer and business publications, ask for a copy of Best Sellers.