Sunscreens with sunprotection factors (SPF) of 100 or more may not provide the protection one might expect.

"Using sunscreen with a high SPF is not an excuse to stay out in the sun longer," said Dr. George Reizner, dermatology professor at the University of Wisconsin School of Medicine and Public Health, on the newest products touting very high SPFs.

"It's dangerous to rely on numbers alone since SPF is only part of the story," Reizner said.

Current sunscreen manufacturers are required only to label products for the amount of UVB protection they provide. UVB is ultraviolet light which commonly causes sun tanning and burns. Reizner said the SPF number does not make clear if it also blocks UVA, light that penetrates deeper into the skin.

Both UVA and UVB cause skin aging and can lead to skin cancer. Newer products do offer "broad spectrum" protection with better UVA blocking, but they still remain less effective compared to how they block UVB.

Add to this the increasing SPF numbers advertised and the public can be confused.

The Food and Drug Administration has proposed a fourstar rating system to tell consumers about the amount of UVA protection in each product. The FDA also is considering a 50 SPF limit on sunscreen products.

"The marketing of highnumber SPF products is a commercial race for bragging rights and promoting more product sales," said Reizner, a practicing dermatologist. "Higher numbers are not necessarily meaningful and do not offer perfect protection."

"Sunscreens are just one leg of the table," Reizner said. "You also should consider your skin type, which type of sunscreen is appropriate for your skin, the clothes you'll be wearing, the time of day, family history of sun damage and skin cancer, and if you're taking medications that make you light-sensitive."

Reizner warns sunbathers and swimmers not to have a false sense of security by using products labeled "waterproof." While many products are water-resistant, none are truly waterproof. Reizner recommends frequently reapplying sunscreen regardless of the company's use directions.

What should the careful sunscreen-shopper look for? Reizner recommends products with zinc oxide or titanium dioxide and those with protection from both UVB and UVA radiation.

"We're living longer and the accumulative effects of sun exposure are creating a skin cancer epidemic, especially melanoma," Reizner said.

This information was provided by University of Wisconsin Hospital and Clinics.