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Most of us know that slathering on sunscreen is important, especially when spending more time outside during the summer months. But knowing what's in the sunscreen that actually protects skin and understanding the products' labeling is often another matter.

An FDA labeling upgrade set to hit over-the-counter sunscreens by fall aims to make sure everybody knows the difference between Ultraviolet-A and Ultraviolet-B radiation, commonly called "UVA rays" and "UVB rays."

For a long time, it was thought the sun's UVB rays, responsible for most sunburn, was a main source of skin cancer. But science shows UVA rays may be even more damaging.

Yet dermatologist Dr. Monica Halem of ColumbiaDoctors EastSide, who is also an assistant professor at Columbia University, notes that there have never been clear guidelines on UVA.

"There's Ultraviolet-A radiation and Ultraviolet-B radiation. UVA radiation is a longer wavelength that actually penetrates through windows and through the clouds," says Halem. "So when you look at a bottle of sunscreen, what it says to you is that SPF factor, or the sun protection factor, is only monitoring UVB radiation."

This labeling question is a common concern among Halem's patients.

"My husband and I had skin cancer two years ago, so it's something that's very obvious to me if you need to take care of yourself," says patient Cheryl Brew. "There are so many products out there that you're never really sure what's really appropriate and what's not."

A four-star rating system showing lowest to highest UVA protection will be implemented by fall. But until then, Halem says there are certain things to look for to select the best protection.

"You want to make sure that your sunscreen has at least SPF 30 or higher," says Halem. "You want, at this point, [a sunblock] that does say 'Broad Spectrum UVA/UVB,' even though we're still awaiting the four-star monitoring system."

Skin care experts say while understanding the labeling on sunscreens is important, proper application must also be understood.

If you don't reapply sunscreen while outdoors, you can still develop serious skin damage.

"Most people don't apply it correctly. About 15 to 30 minutes prior to when you go outside, you want to apply sunscreen," says Halem. "And then you want to re-apply it every two hours."

Also keep in mind that despite some labeling, no sunscreen is waterproof, and some water-resistant. This point will also be clarified on products by fall. Until then, if you sweat or take a dip in the water, be sure to reapply sunscreen.