If the UV index is high, it's crucial you wear sunscreen, seek shade, and cover up in protective clothing.SupergoopRadiation from the sun's ultraviolet (UV) rays can cause lasting damage to your skin. In fact, UV rays are the leading cause of skin cancers, like melanoma and basal cell carcinoma, says Beth Goldstein, MD, a dermatologist with Central Dermatology Center.Therefore, it's important to monitor the UV index in your area before spending time outside.