Ultraviolet radiation, often called ultraviolet light (although it's invisible to the human eye) is a type of ionizing radiation. It describes frequencies of the electromagnetic spectrum that are slightly higher than those of the visible color violet.
Prolonged exposure to ultraviolet radiation, which is a natural component of sunlight, puts a person at higher risk of skin cancer.
Ultraviolet radiation is blocked by clear glass and zinc oxide ointments. Melanin, a skin pigment, also effectively reduces ultraviolet exposure. Most people produce melanin ("tanning") in response to exposure to ultraviolet radiation.