When sunscreen is on your shopping list, what do you look for?

If the lotion's SPF, or sun protection factor, leads your purchasing decision, you're like half of the 1,000 adult sunscreen wearers in the United States recently surveyed by the Consumer Reports National Research Center.

Consumer Reports researchers tested 20 sunscreens, according to a news release, and even though they honed in on several to recommend, only two sunscreens provided the SPF protection after water immersion promised on their packages.

In fact, one product came in at less than half of its claimed SPF, while another didn't sport a rating and Consumer Reports was unable to track it down because the particular lotion was marketed for use on children.

The protection results of the other lotions came in between 4 to 40 percent below their claims.

Of course, even an SPF 30 sunscreen that comes in, say, 40 percent below its claim still provides an SPF of 18, notes a Consumer Reports statement.

Consumer Reports says it can't offer a specific reason for the differences between its test results and manufacturer claims, "but they show that SPF isn't always carved in stone." The tests conducted by Consumer Reports discovered a wide variability of effectiveness against UVA rays.

The findings of the survey underscore the importance of choosing from our recommended sunscreens. If none are available, a product rated Good will provide adequate protection. Using any sunscreen is better than using none, but it's just one part of a smart sun-protection strategy.

The top recommended sunscreens were Equate Ultra Protection SPF 50 from Walmart and Up & Up Sport SPF 50 spray from Target.

Other lotions deemed by Consumer Reports worth mentioning are BullFrog Water Armor Sport InstaCool SPF 50+ spray, Coppertone Water Babies SPF 50 lotion, Banana Boat Ultra Defense Max Skin Protect SPF 110 Spray and Neutrogena Ultimate Sport SPF 70+ lotion.