You’re probably aware that tanning contributes to skin aging and the development of skin cancers, as well as damage to the eyes and immune system. But now there’s more bad news: it may be addictive, too.

• A sun protection factor (SPF) of 15 or greater
• Validation of the SPF number by testing on 20 people
• Acceptable test results for phototoxic reactions and contact irritation
• Substantiation for any claims that a sunscreen is water- or sweat-resistant

Summer's here, and that means outdoor sports and social events, and, if you're not careful, sun damage. The sun's ultraviolet radiation (UVR) accelerates skin aging and increases the risk of skin cancer, cataracts, and other eye diseases. But some simple strategies can help you maximize summer fun without sacrificing your health.

For example, when you're running, hiking or biking, use a sport (usually stick) sunscreen formula on your face - it won't run into your eyes when you heat up. Reapply often if you sweat heavily.

Beachgoers and water enthusiasts have special concerns, since both water and sand reflect up to 80 percent of the sun's rays, adding to your overall exposure. If you're swimming, apply a full ounce (two tablespoons) of water-resistant sunscreen 30 minutes before sun exposure, and reapply immediately after swimming. Sailors face this added, reflected exposure not only from the water, but also from a sailboat's white sails. In addition to using sunscreen, protect your eyes with wraparound, UV-blocking sunglasses. A broad-brimmed hat and bright- or dark-colored long sleeves and pants will also shield your skin.

For surfers, neoprene (synthetic rubber) and UV-protective Lycra wetsuits offer sun protection in cold or warm water. A nylon or neoprene surfing cap that covers the scalp and ears is also a good idea. You may prefer an alcohol-based gel or spray sunscreen for exposed trouble spots like the top of the head and scalp.

If you're just lounging in the sand, stay under sun umbrellas or portable shade structures. Some come with a UPF (Ultraviolet Protection Factor) label. UPF numbers indicate how much of the sun's radiation the fabric will absorb; a UPF of 30 means just 1/30th of the sun's rays penetrate the fabric. The Skin Cancer Foundation recommends UPFs of 30 or higher.

Group events - from tennis and golf to barbecues - should be scheduled when the sun is weakest: before 10AM or after 4PM. Evening activities allow you to avoid the midday heat, and the later sunsets provide light long into the evening hours.

Finally, if a family vacation involves a long car trip, consider installing UV film on your car windows to block harmful UVA rays and reduce glare.

Please take these tips to heart, and have a happy and healthy summer!

Perry Robins, MD, President

© 2008, The Skin Cancer Foundation, Inc. All rights reserved.

In this section, physicians belonging to The Skin Cancer Foundation's lifetime membership group, The Rex and Johnnie Amonette Circle, answer questions from the public. Our guest physician is Karen E. Burke, MD, PhD, Department of Dermatology, Mt. Sinai Medical Center, New York City, and author of Great Skin for Life and other books.

Q: Does a sunscreen become ineffective with age? How long can I keep a sunscreen before I have to throw it out?

A: Expiration dates are often stamped on sunscreen containers to specify the time limit for a product's stability and efficacy. For optimal sun protection as well as texture, stability, and sterility, use the sunscreen prior to the date listed. If you can't find a date on a new tube or bottle, write the month and year you purchased it in permanent marker on the tube.

To test shelf life, manufacturers store a product at 40°C with 75 percent humidity; then at 40°C with 25 percent humidity; and then test it at 0, 1, 2, and 3 months. Stability for three months in these laboratory conditions is comparable to three years in normal ambient environments. So your sunscreen should be good for up to three years after purchase.

Of the 17 sunscreen ingredients approved in the U.S., 15 are organic, or chemical, sunscreens: They work by absorbing damaging ultraviolet radiation (UVR). These chemical sunscreens consist of innately unstable molecules, but in the past few years manufacturers have started adding stabilizers like octocrylene.

Zinc oxide and titanium dioxide are physical, inorganic sunscreens; they reflect and diffuse UVR. Both are photostable and do not change molecular structure when exposed to UVR. Physical sunscreens once had an opaque, paste-like consistency, but in the past two decades manufacturers have developed cosmetically elegant formulations using micronized (tiny) particles. Since micronized titanium dioxide and zinc oxide can clump together over time, often the particles are coated with dimethicone or silica to keep the ingredients stable and smooth. And in addition to active compounds, sunscreens usually contain preservatives, emulsifiers, fragrances, and other additives.

Sunscreens are tested in their actual containers, since plastics in the container may leach into the sunscreen and cause a chemical interaction. UVR changes the molecular structure of chemical sunscreens, so sunscreen containers should be opaque.

For best results, use your sunscreen before the stated expiration date, and store it in a cool place.

For more skin protection information, click on Prevention Guidelines.