Ultraviolet (UV) rays are a type of electromagnetic radiation that has shorter wavelengths than visible light. UV rays are invisible to the human eye, but they can cause damage to the skin and eyes if exposure is too high. UV rays are divided into three categories: UVA, UVB, and UVC. UVA and UVB rays are the most common and can cause sunburns, wrinkles, and other skin damage. UVC rays are the most dangerous, but are mostly blocked by the atmosphere.