Henna dyes hair, skin, and fabric organically, similar to a black tea dye. Henna is extracted from a tree by drying and grinding leaves and stems. The greenish powder, when mixed with an acidic liquid, makes a temporary red, brown, or orange design on a porous surface. People use henna in ritual skin painting, called Mehndi, for birth and marriage celebrations. Western cultures have adopted henna to make temporary tattoos and organic hair dye.
The henna tree, Lawsonia inermis, grows in hot, arid regions like North Africa and India. For centuries, people ground the foliage of the plant into a powder to dye cloth and skin. The strong pigment, lawsone, actually temporarily stains the skin. Lawsone is a tannin; tannins are also found in wine and tea. They infuse porous surfaces with a darker pigment, but do not chemically alter the surface permanently.
Henna works because lawsone is absorbed into material like hair and skin. You mix the powdered henna into a mud, using hot water, lemon juice, vinegar, or other acidic additives. An acidic mixture strengthens the dyeing properties. Then you apply the henna mud to a surface like the palm of your hand, bottom of your feet, or anywhere on your body. Leave the mud on for as long as possible, up to 48 hours. When it dries and crumbles off, the skin will have darkened to auburn, orange, red, or brown.