For effective protection, dermatologists generally recommend using a sunscreen with an SPF of at least 30. SPF 30 blocks about 97% of UVB rays, while SPF 50 blocks about 98%. Higher SPFs provide marginally better protection, but no sunscreen can block 100% of UV rays. It is also important to apply sunscreen generously and reapply every two hours, or more often if swimming or sweating.
