What You Need to Know About Sun Safety Skin cancer is the most common cancer in the U.S. Too much sun can cause skin cancer, which can be disfiguring and even deadly. Unprotected skin can be damaged by the sun’s UV rays in as little as 15 minutes. Damage from exposure to UV rays builds up over a lifetime. Even on cloudy days, UV rays are present and can be reflected from water, sand, and snow. Stay in the shade, especially during midday. Wear a hat with a wide brim to shade your face, head, ears, and neck. Wear sunglasses that block UVA and UVB rays. Wear clothing that covers your arms and legs. Every 2 hours, apply sunscreen with SPF 15 or higher and UVA and UVB (broad-spectrum) protection. Reapply sunscreen after swimming, sweating, or toweling off. To learn more, visit cdc.gov/cancer/skin