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.

Depending on the fineness of the paste, you can apply henna with a tube, like icing a cake. With a lot of coordination and care, people can achieve intricate designs full of scrolls, swirls, paisley outlines, and dots. Henna tattoos create temporary bracelets, motifs, emblems, or words. In traditional Mehndi, Muslims and Hindus decorate the skin of those participating in special ceremonies, such as a wedding or circumcision, in places like Indonesia and India.

Dying with henna is entirely temporary. Hair dye may last up to six weeks, but skin dye will probably not stay visible for more than a week. This is because the dye has only sunken into the uppermost layer of dead and dying skin. When your skin flakes off through natural exfoliation, it will be gradually replaced by fresh skin of your natural color. Henna hair dye will also slowly fade away to your hair's original color, but will not leave any lines or stripes like synthetic dye.