Most people know that SPF stands for sun protection factor and that few users apply enough sunblock to do the trick. What you might not know is that the SPF pertains only to UVB rays. “There is no standardized way to quantify a product’s ability to protect against damage from UVA rays,” says Dr. Michelle Yagoda, a New York City-based plastic surgeon and co-founder of Beautyscoop. “In simple terms, it doesn’t matter what the SPF number is, you probably don’t have enough protection from the sun’s damaging UVA rays.”

Dr. Yagoda gives us the low-down on effective sun protection:

UVA vs. UVB: What’s the difference? The sun’s UVB rays are the milder, tanning” rays, but the UVA rays are the aggressors — causing premature aging, sun spots and skin cancers. While there is currently no rating scale to assess sun protection from UVA rays, you can choose a product labeled with the words “broad spectrum UVA/UVB” to provide you with the ssurance you are looking for. A simple “UVA/UVB” label is not enough, as it only  indicates that there is some, limited UVA protection.