Remember how much a blistering sunburn hurt as a child? Medical experts now believe that too much exposure to the sun as a child and teenager is a major cause of skin cancer and premature skin aging.

But regular sun exposure throughout the year also contributes to long-term skin damage. Tanning, for example, is a sign of skin damage. Even children with darker complexions, who have more natural protection against the sun, are at risk.

Two kinds of ultraviolet sun rays, UVA and UVB, can cause skin damage. This can range from immediate effects such as burning, photosensitive reactions (rashes), and cell and tissue damage to long-term consequences such as wrinkling and skin cancer. Experts believe that UVA also may weaken the immune system.

You can help protect your child's skin from damage by taking the right steps early.

Using sunscreens is important. Many dermatologists believe children and teenagers who regularly use suncreens can significantly reduce the risk of skin damage, including skin cancer, later in life.

* Use waterproof or water resistant sunscreens that help to protect skin from both UVA and UVB rays and have SPF (sun protection factor) numbers of at least 15.

* Apply sunscreen liberally (at least one large handful for a body) about 30 minutes before going outside. No matter what sunscreen product is used, be sure it is reapplied after swimming or perspiring heavily.

* Talk with camp counselors and others with child care responsibilities about reapplying sunscreens. Toweling off after swimming, for example, will remove even waterproof sunscreens.

Know that no sunscreen totally blocks the sun's rays. Even children wearing high SPF sunscreens get some exposure to ultraviolet rays.

To help protect children from the sun, you may want to keep in mind the following.

* When scheduling children's outdoor activities, remember the sun is strongest from 10:00 am to 3:00 pm.

* Dress children for maximum protection against the sun. Hats with brims and tight-weave long-sleeved shirts and pants offer the best protection.

* Sunglasses can help protect children's eyes. Select sunglasses that help to screen out both UVA and UVB rays. UV rays may contribute to the development of cataracts. Sunglasses that are close-fitting to the face and with larger lenses also can give more protection.

* Teenagers who work outside in such jobs as lifeguards, gardeners, or construction workers may be at special risk for skin damage. They need adequate protection before going out in the sun.

* Discourage teenagers from going to tanning parlors. Tanning devices can damage the skin and eyes as much as direct sunlight.

* Keep babies younger than six months out of the sun. Know that sunscreens may irritate baby skin, and an infant's developing eyes are especially vulnerable to sunlight.

Medical experts believe that the sun causes most skin cancer, which is the most common form of cancer in this country. More younger people now are being diagnosed with it.

Two types of skin cancer, basal cell and squamous cell, will develop this year in more than three-quarters of a million Americans. If detected early, these cancers are usually treatable.

The third kind of cancer, melanoma, is more deadly, and its incidence is increasing faster than any other form of cancer. Early detection is crucial for successful treatment.

Several factors are associated with increased risk of developing skin cancer. These include having:

* Several blistering sunburns as a child or teenager.

* A family history of skin cancer.

* Light-colored skin, hair, and eyes.

* Difficulty tanning or frequent sunburns.

* Moles that: are irregular in shape or color; change in size, shape, or color; or itch or bleed.

Be sure to check with your family doctor or dermatologist if you have questions or concerns about skin cancer or skin damage. For free FTC brochures, such as Sunscreens, Indoor Tanning, or Best Sellers (which lists more than 140 brochures on many consumer topics) contact: Public Reference, Federal Trade Commission, Washington, DC 20580; (202) 326-2222. TDD: (202) 326-2502.