Henna is a small tree, and its leaves contain a dye which stains your skin – similar to turmeric or beets. However, with henna, the dye molecule (lawsone) binds to the keratin in your skin, which makes it a permanent stain!
Henna can also refer to the temporary body art resulting from the staining of the skin from the dyes (see also mehndi). After henna stains reach their peak color, they hold for a few days, then gradually wear off by way of exfoliation, typically within one to three weeks.
Mehndi is a form of body art and temporary skin decoration originating in ancient India, in which decorative designs are created on a person’s body, using a paste, created from the powdered dry leaves of the henna plant (Lawsonia inermis). Dating back to ancient India, mehndi is still a popular form of body art among the women of the Indian subcontinent, Bangladesh, Pakistan, Nepal, the Maldives, Africa and the Middle East. In the late 1990s, mehndi decorations became fashionable in the West, popularized by Indian cinema and entertainment industry, where they are called henna tattoos.
Henna has been used since antiquity to dye skin, hair, and fingernails, as well as fabrics including silk, wool and leather.