A sunscreen is a topical product used to protect the skin from the harmful effects of the sun's ultraviolet (UV) rays. It contains chemical or mineral filters that absorb, reflect, or scatter UV rays. Sunscreens are rated by their sun protection factor (SPF), which indicates how effective they are at preventing sunburn. Regular use of sunscreen helps prevent sunburn, premature skin aging, and reduces the risk of skin cancer. It is recommended to choose a broad-spectrum sunscreen for protection against both UVA and UVB rays.