Do you need SPF 30, 50 or 100? Dermatologists answer your burning sunscreen questions

Dermatologists clarify that SPF numbers measure protection against ultraviolet B (UVB) rays, the primary cause of sunburns. SPF 30 filters about 97% of UVB rays, while SPF 50 blocks 98%, and SPF 100 only adds a marginal 1% more protection. Dr. Adewole Adamson from the University of Texas at Austin and Dr. Marisa Garshick from New York Presbyterian-Weill Cornell Medicine emphasize that higher SPF provides a safety buffer for underapplication but does not guarantee full protection. The U.S. Food and Drug Administration (FDA) defines SPF as the ratio of solar energy needed to burn skin with sunscreen compared to skin without it. Experts advise using at least SPF 30, as lower SPFs offer less protection and may not compensate for inadequate application. Garshick notes that SPF 100 does not block 100% of UVB rays, and the FDA banned the term 'sunblock' in 2011 due to this limitation. Sunscreen should be broad-spectrum to protect against both UVA and UVB rays, as UVA rays contribute to wrinkles and skin cancer. Water-resistant formulas are recommended for swimming or sweating. Adamson stresses that sunscreen must feel comfortable to ensure consistent use, as effectiveness depends on proper application. Higher SPF sunscreens may cost more but provide diminishing returns in protection. UC Davis Health reports that the incremental benefit from SPF 50 to SPF 100 is minimal if applied correctly. Garshick warns that higher SPFs can create a false sense of security, encouraging users to skip reapplication or use less product.