As the Memorial Day weekend begins, many Americans are confused about the proper application of sunscreen and about its sun protection factor (SPF), the American Academy of Dermatology says.

A recent academy poll of 1,000 U.S. adults revealed that while 80 percent know they should apply sunscreen every two hours when outdoors, only 33 percent typically do so, while 42 percent typically do not reapply it at all or reapply it only when they get wet. Furthermore, three in 10 respondents said they apply sunscreen only to their face, leaving other areas of their body unprotected.

A recent report in the journal JAMA Dermatology showed that most Americans consider the SPF rating to be the most important criteria when selecting sunscreen.

"There is a lot of information on sunscreen labels, and one piece of information isn't necessarily more important than another," said Henry Lim, M.D., former chair of the department of dermatology at Henry Ford Hospital in Detroit. "I tell my patients to look for three things when choosing a sunscreen -- SPF 30 or higher, broad-spectrum protection, and water resistance."

An SPF 30 sunscreen blocks 97 percent of the sun's ultraviolet B (UVB) rays, and higher-number SPFs block slightly more of those rays, but no sunscreen can block 100 percent of the sun's UVB rays.

"Reapplication is key, along with understanding SPF," Lim said in an AAD news release. "Many people mistakenly assume that they can apply the sunscreen with the highest SPF rating and then stay out in the sun all day without reapplying; however, SPF is a measurement of how well a sunscreen protects the skin from the sun's UVB rays, which cause sunburn. It is not a measurement of how long someone can stay in the sun or how frequently it needs to be applied."

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