How does tanning work?

Tanning beds use ultraviolet (UV) light to tan the skin. There are three types of UV light: UVA, UVB, and UVC. Tanning beds are designed to concentrate optimal levels of UVA along with very low percentages of UVB on the outermost layers of skin. This stimulates the production of melanin pigment, which is slightly pink in its dormant state, and causes it to turn brown after excretion. The amount of melanin cells present in the skin determines the amount of pigment that will be excreted and distributed, thus affecting how tan the skin will become. Tanning beds are designed to filter out UVC, which is a harmful type of UV light.