Ultraviolet radiation, often called ultraviolet light (although it is 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.
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.