Henna

The plant

Henna (Lawsonia inermis) is a flowering plant of the family Lythraceae. It is a tall shrub or small tree, standing 1.8 to 7.6 m tall. The henna plant is native to northern and eastern Africa, Asia and northern Australia, in semi-arid zones and tropical areas.

The dye

The dried leaves of the henna plant are the source of the dye used on skin, hair and fingernails, and on fabrics including silk, wool and leather. Lawsone (2-hydroxy-1,4-naphthoquinone) is a red-orange dye present in the leaves of the henna plant. Whole, unbroken henna leaves will not stain the skin because lawsone is bound within the plant. Dried henna leaves will stain the skin if they are mashed into a paste. Henna stains are orange when the paste is first removed but darken over the following three days to a deep reddish brown due to oxidation. The stain gradually wears off by exfoliation, typically within one to three weeks.

Chemistry

A total of 72 components were identified in the headspace of different henna samples, which differed considerably from each other. They were mainly aliphatic compounds, terpenoids and aromatics. Major representatives include limonene, carvol, geranyl acetone and (E)-caryophyllene. Alpha-ionone is recorded in the flower at 20.0 to 40.0 parts per million, and in the flower essential oil at a high value of 180000.0 parts per million.

History and use

The origins of the initial human uses of henna are uncertain. Henna was used in Ancient Egypt on some mummies to dye their hair, skin, nails, or funeral wrappings. Pliny the Elder wrote about its use in the Roman Empire as a medicine, a perfume, and a dye. In India, henna was in use by the 4th century CE, which is evidenced by the cave art of the Deccan region. Mehndi is a form of temporary skin decoration using a paste created with henna. In the Indian Subcontinent, mehndi is traditionally applied during many celebrations, especially weddings, religious festivals, and family ceremonies. The term mehndi derives from the Sanskrit word mendhikā, which refers to the henna plant.

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