Fresh henna leaves cannot stain skin until they are crushed
The dye in henna, a molecule called lawsone, stays locked inside intact leaves. Only when dried leaves are ground and mixed into a paste does it seep into the outer skin and bind to proteins there. The stain starts orange and darkens over about three days to a deep reddish brown.
Henna comes from the powdered leaves of Lawsonia inermis, and its name derives from the Arabic ḥinnāʾ. Its first human use is uncertain, but the plant was traded in Babylonia and used in ancient Egypt on some mummies. The mummy of Ahmose-Henuttamehu, a 17th Dynasty royal dated to 1574 BC, had hair dyed bright red at the sides, probably with henna. Pliny the Elder described Romans using it as medicine, perfume and dye.
Preparing it is a craft. Powder is mixed with water, lemon juice or strong tea, often with sugar or molasses for stickiness, then left for one to 48 hours so the lawsone can release. Tools vary by region: a twig, a syringe in Morocco, a piping cone in India. Palms and soles, where skin is thickest, take the darkest and longest-lasting colour. A leaf holds only so much lawsone, so mixed paste stays active for just two to six days, though freezing preserves it for up to four months.
As body art it is ancient. Frescoes at Akrotiri, painted before Thera erupted in 1680 BC, depict women whose nails, palms and soles bear henna-like marks, and the Ugaritic legend of Baal and Anath mentions women hennaing themselves before meeting their husbands. The Night of the Henna before a wedding was kept by Jews, Muslims, Sikhs and Hindus alike, and festivals from Diwali to Eid and Passover featured it. Favourite horses, donkeys and salukis sometimes had hooves, paws or tails dyed as well.
Henna was believed to carry barakah, blessing, so brides received the most elaborate designs; in Yemen, the Jewish bridal process could last four or five days. In Europe it became fashionable in the 1800s among Pre-Raphaelite circles, and the opera singer Adelina Patti is sometimes credited with popularising it. The Parisian courtesan Cora Pearl claimed to have dyed her dog to match her own red hair.
Source: Henna
