Sunscreens and SPF numbers can be confusing. Here are some sun safety basics.

By now most of us know that wearing sunscreen is Rule #1 for skin protection. We know that sunburn raises the risk of skin cancer, and that sun damage leads to wrinkles, spots and other less-than-lovely things. But do we know the ins and outs of SPF and how to apply the best protection? Not according to a 2016 survey by the American Association of Dermatology (AAD) that found that 68 percent of those polled thought that SPF 30 provided twice the protection of SPF 15. (It does not: both provide roughly two hours of coverage).

According to the AAD, a higher SPF does NOT indicate longer effectiveness, but rather a higher percentage of UVB ray protection. For example, SPF 15 blocks 93 percent of the sun’s UVB rays, while a SPF 30 blocks 97 percent, and a SPF 50 bumps that up to 98 percent.

Three things to keep in mind when choosing a sunscreen:

1. Go Broad

As in broad-spectrum. A broad-spectrum sunscreen protects against both ultraviolet A (UVA) and ultraviolet B (UVB) rays. The difference is that UVB rays cause sunburn, while UVA rays lead to wrinkles and changes in pigmentation. Most importantly – both can result in skin cancer.

2. 30 Rocks

Experts recommend applying at least a SPF 30 or higher. A broad-spectrum SPF 30 blocks out 97 percent of the rays. Don’t skimp! And remember too that the best protection is to wear long sleeves and pants, a hat and stay out of the sun as much as possible.

3. Reapply Often

And at least every two hours. And be sure to reapply after swimming and toweling off.