SPF

SPF (Sun Protection Factor) measures a sunscreen's ability to protect skin from UVB rays, which cause sunburn and skin cancer. It indicates how much longer it takes for skin to burn with sunscreen compared to without it. Experts recommend at least SPF 30, which blocks roughly 97% of UVB rays. Key Aspects of SPF Protection Level: SPF 15 blocks ~93%, SPF 30 blocks ~97%, and SPF 50 blocks ~98% of UVB rays. Not a Time Metric: While often linked to time (e.g., SPF 30 allows 30 times longer exposure), SPF is more accurately a measure of solar energy protection. Reapplication: Sunscreen should be reapplied every two hours, or after swimming/sweating, regardless of the SPF number. Broad Spectrum: Always choose "broad spectrum" sunscreen, which protects against both UVA (aging) and UVB (burning) rays. Limitations: No sunscreen blocks 100% of UV rays, and higher SPF numbers (over 50) offer only marginal additional protection,