When it comes to sunscreen SPF is important. But it's not the whole story. SPF is an indicator of how well a lotion protects skin from the sun's UVB rays. These are the rays that lead to sunburn. But there's the catch. Scientists now know it's also important to shield yourself from UVA rays. Both sets of rays can cause skin cancer and aging. That's why there's a push for more UVA protection.

To make sure you're getting sunscreen with UVA protection, there are a few ingredients to look for. The most common one is a chemical called avobenzone. It shows up on labels under the name Parsol 1789, and products that contain it often say "broad-spectrum protection" on the front of the bottle.

The problem with these sunscreens is that they just don't hold up on the skin very long. They degrade quickly, so the UVA protection is not so robust, Most sunscreens wear off after two hours, some products are better than others. Instead of mere sunscreens, sunblocks are preferred, particularly ones made with titanium dioxide or zinc oxide. The traditional notion of a sunblock may conjure of the lifeguard with the white nose sitting under the umbrella. That's the old way of using zinc oxide. But in recent years, the zinc has been broken down into finer particles, so there's no visible glob of white on your skin. These products are gentler on the skin, and they protect against the sun by actually blocking and scattering the light.

These new sunblocks "have a fairly broad range of UVA and UVB protection, and they tend to be less irritating, particularly for people with sensitive skin. Two newer options for longer-lasting protection are sunscreens made with stabilizing technologies that keep the active ingredients from breaking down. One of the products is called "Helioplex." And the other, sold in Europe as Mexoryl, is beginning to make its way to the United States. These products may last about four hours, twice as long as traditional sunscreens. The advantage of the Helioplex technology, as well as the Mexoryl, is that you don't have to reapply every two hours.

Perhaps the most important thing when it comes to sunscreens is to put on enough lotion. A full ounce is the recommended amount. A shot glass holds an ounce of fluid. That is what it takes to cover your body at the pool. Once it's spread out all over his body, a shot-glass-full isn't so much.

Here's a trick, if you want to get away with less: crank up the SPF. A half-ounce of an SPF 50 lotion is almost like using a full ounce of SPF 25.

In the near future, there may be an easier way to determine whether a particular sunscreen has UVA and UVB protection. The Food and Drug Administration is drafting a new regulation. It will build on the SPF rating system by adding a pass/fail rating for UVA rays.