Harvard Women's Health Watch

By the way, doctor: What's in sunscreen that protects against UVA rays?

Q. What UVA-blocking ingredients should I look for in a sunscreen? And does a higher SPF rating mean greater UVA protection?

A. The sun emits three types of ultraviolet rays, distinguished by wavelength ranges: ultra violet A (UVA) is the longest; ultraviolet B (UVB) radiation is medium-wavelength; and ultraviolet C (UVC) has the shortest wavelength range. UVC rays never touch our skin. UVB rays are the main cause of sunburn, and UVA rays penetrate the skin more deeply and contribute to skin aging; both types can cause skin cancer. An effective sunscreen should block both UVA and UVB.

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