Updated: December 08, 2016

Dermatologist Doris Day, MD, a professor at NYU Medical School, answers a Health magazine reader's question about sun protection.

Q: I’ve noticed a lot of sunscreens touting sky-high SPFs like 70 and 80. Do they work better than lower numbers?

A: They do work slightly better—if used properly. Let me explain: An SPF 15 blocks 93 percent of UVB rays, SPF 30 shields 97 percent, and SPF 50 fends off 99 percent. (SPF measures only UVB protection, so scan labels for terms like “UVA/UVB protection” or “broad-spectrum protection” to ensure your sunscreen also guards against UVA rays.) The difference between these numbers may seem small, but it can be significant for people who are sensitive to the sun (i.e., those who are fair-skinned, prone to skin cancer, or have melasma or other pigmentation problems); they should absolutely choose a sunscreen with the highest possible SPF. Everyone else should look for photostabilized formulas (meaning their UV filters don’t break down as rapidly), no matter what the SPF. Coppertone, Aveeno, Neutrogena, and Banana Boat all offer high-SPF products with stable broad-spectrum protection.

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