Henna is a dye made from dried, powdered leaves of Lawsonia inermis, used to produce reddish stains used in body art. It originates in North Africa and the Middle East, and has been used since at least antiquity across the region, including in ancient Egypt, as well as in ancient Mesopotamia and broader pre-Islamic Arabian cultures, as a hair and body dye, notably in the temporary body art of mehndi (or “henna tattoo”) resulting from the staining of the skin using dyes from the henna plant. After henna stains reach their peak colour, they hold for a few days and then gradually wear off by way of exfoliation, typically within one to three weeks.

Henna has been used in ancient Egypt, ancient Near East and the Indian subcontinent to dye skin, hair, and fingernails; as well as fabrics including silk, wool, and leather. Historically, Henna originates from North Africa, particularly ancient Egypt and the Maghreb (including present-day Morocco, Algeria, and Tunisia), as well as from the Middle East, including the Arabian Peninsula and West Asia. From these regions, its use gradually spread to Carthage and other parts of West Africa, Central Africa, the Horn of Africa, and later to the Indian subcontinent.

The name henna is used in other skin and hair dyes, such as black henna and neutral henna, neither of which is derived from the henna plant.

The word henna comes from the Arabic حِنَّاء‎ (ALA-LC: ḥinnāʾ; pronounced [ħɪnˈnæːʔ]).

The origins of the initial human uses of henna are uncertain; however, there are records that the plant was marketed in Babylonia, and was used in Ancient Egypt on some mummies to dye their hair, skin, nails, or funeral wrappings. It arrived in the Maghreb region during the Punic civilization through Phoenician Diasporas where it was used as a beautification tool. Pliny the Elder wrote about its use in the Roman Empire as a medicine, a perfume, and a dye.

Whole, unbroken henna leaves will not stain the skin because the active chemical agent, lawsone, is bound within the plant. However, dried henna leaves will stain the skin if they are mashed into a paste. The lawsone will gradually migrate from the henna paste into the outer layer of the skin and bind to the proteins in it, creating a stain.

Since it is difficult to form intricate patterns from coarsely crushed leaves, henna is commonly traded as a powder made by drying, milling and sifting the leaves. The dry powder is mixed with one of a number of liquids, including water, lemon juice, strong tea, and other ingredients, depending on the tradition. Many artists use sugar or molasses in the paste to improve consistency to keep it stuck to the skin better. The henna mix must rest between one and 48 hours before use in order to release the lawsone from the leaf matter. The timing depends on the crop of henna being used. Essential oils with high levels of monoterpene alcohols, such as tea tree, cajuput, or lavender, will improve skin stain characteristics. Other essential oils, such as eucalyptus and clove, are not used because they can irritate the skin.

The paste can be applied with many traditional and innovative tools, starting with a basic stick or twig. In Morocco, a syringe is common. A plastic cone similar to those used to pipe icing onto cakes is used in India. A light stain may be achieved within minutes, but the longer the paste is left on the skin, the darker and longer lasting the stain will be, so it needs to be left on as long as possible. To prevent it from drying or falling off the skin, the paste is often sealed down by dabbing a sugar/lemon mix over the dried paste or adding some form of sugar to the paste. After some time, the dry paste is simply brushed or scraped away. The paste should be kept on the skin for a minimum of four to six hours, but longer times and even wearing the paste overnight is a common practice. Removal should not be done with water, as water interferes with the oxidation process of stain development. Cooking oil may be used to loosen dry paste.