The sun reaches us with two types of harmful rays: long wave ultraviolet A (UVA) and short wave ultraviolet B (UVB).
UVA rays pass through the earth's atmosphere and straight through the ozone layer and penetrate deep into the skin. Studies have shown UVA rays heavily contribute to premature aging, causing up to 90% of the aging of your skin. While the ozone layer partially absorbs UVB rays, mostly affect the surface of the skin and are the primary cause of sunburn.
Selecting a broad spectrum sunscreen is essential for your protection from both UVA and UVB rays. Even with a high SPF (sun protection factor), if a sunscreen isn’t broad spectrum, you won’t be protected. Look for for sunscreens labeled broad spectrum.
Another useful way to remember:
UVB has a B for “burning” – cause sunburn, aging, and potentially skin cancer
UVA has an A for “aging” - cause wrinkles