Sunscreens

The single most important cause of premature skin aging and wrinkles is sun exposure, especially early in life. Sun damage also increases the risk for skin cancer. For these reasons, a good sunscreen is the most important skin cream you can buy.

* The sun and wrinkles. Sun damage to the skin is caused by different wavelengths of ultraviolet (UV) radiation, which penetrate the skin to different depths and appear to harm cells in different ways. UV radiation is thought to promote the release of oxidants, which, in excess, can damage cell membranes and contribute to wrinkling. Researchers are investigating whether some UV rays mainly cause wrinkles and lentigines, or liver spots, and others speed the development of skin cancer.

Even in small amounts, sunlight sets in motion a series of wrinkle-inducing events. It damages collagen fibers, which give the skin its strength and firmness, and causes abnormal elastin (a protein that contributes to the skin's elasticity) to accumulate. In response, enzymes are released to help remodel the UV-damaged tissue. But some of these enzymes actually disrupt the process, forming solar scars instead. Eventually, these help form wrinkles and cause saggy skin.

* Deflecting the sun's damage. Sun blocks are highly effective in protecting against the two main types of UV radiation, UVA and UVB rays. Zinc oxide and its chemical cousin, titanium dioxide, are sun blocks because they actually stop ultraviolet radiation from reaching your skin. Both are available in skin tones and other colors, and titanium dioxide is available in a clear formula. These ingredients are used in some commercial lotions, such as the so-called "non-chemical" sun blocks. Sunscreens, on the other hand, absorb rather than block UV rays. At one time, most sunscreens relied on para-aminobenzoic acid, or PABA, as their main ingredient. But PABA can provoke allergic reactions, so most sun-screens contain instead benzophenones, which protect against UVA; salicylates, which protect against UVB; or cinnamates, which may protect against both. You'll see these listed as active ingredients on sunscreen labels -- for example, as oxybenzone, octyl salicylate, or octyl methoxycinnamate.


A laundry additive, Rit Sun Guard, is now available that washes UV protection into clothing.

* What to buy. When choosing a sunscreen, most people look at the product's sun-protection factor (SPF) rating. The American Academy of Dermatology (AAD) recommends using sunscreen with an SPF rating of at least 15. The higher a sunscreen's SPF rating, the more protection it offers against UVB. The AAD and federal public-health agencies also advise using a broad-spectrum sunscreen that protects against both UVB and UVA rays. While good methods exist for measuring how well a sunscreen protects against UVB, the same isn't true for UVA. Also, it's not known how broad a spectrum of UV radiation is covered by these products. This is an issue the FDA is grappling with in developing new sunscreen-labeling regulations.

* How to use it. About an ounce (2 tablespoons) of sunscreen provides adequate coverage of exposed areas of the body. Apply a water-repellent base about 15 - 30 minutes before going outdoors, and reapply immediately after swimming, or every 2 hours if you stay out of the water. In fact, the AAD says that people who wait more than 2-1/2 hours to reapply have five times the chance of getting sunburned as those who reapply every 2 hours.

From Harvard Women's Health Watch. Copyright 2003 by President and Fellows of Harvard College.