SPF, or Sun Protection Factor, measures how well a sunscreen protects the skin from harmful ultraviolet (UV) rays. The higher the SPF number, the greater the protection. For example, SPF 30 blocks about 97% of UVB rays, while SPF 50 blocks about 98%. It’s important to apply sunscreen generously and reapply it every two hours, especially after swimming or sweating. Using sunblock is essential to prevent skin damage, including sunburn and long-term issues like skin cancer. It is recommended to use a broad-spectrum sunscreen that protects against both UVA and UVB rays for comprehensive skin protection during outdoor activities.