SPF stands for “sun protection factor,” but SPF only indicates protection against UVB, or “burning” rays. It may seem like an SPF of 50 provides almost double the protection as SPF 30, but that’s not the case. SPF 30 blocks 97% of UVB rays6 and SPF 50 blocks 98% of UVB rays.
Since SPF only applies to UVB rays, it’s imperative to choose a sunscreen that says “broad spectrum” on the label, as this indicates the product helps protect the skin from UVA rays as well. Remember, a higher SPF does not mean you can spend more time outside without reapplying.