Henna can also refer to the temporary body art resulting from the staining of the skin from the dyes.
Natural henna produces a rich red-brown stain which can darken in the days after it is first applied and last for several weeks. It is sometimes referred to as “red henna” to differentiate it from products sold as “black henna” or “neutral henna,” which may not actually contain henna, but are instead made from other plants or dyes.
Neutral henna does not change the color of hair. This is not henna powder; it is usually the powder of the plant Senna italica (often referred to by the synonym Cassia obovata) or closely related Cassia and Senna species.
Black henna powder may be derived from indigo (from the plant Indigofera tinctoria). It may also contain unlisted dyes and chemicals such as para-phenylenediamine (PPD), which can stain skin black quickly but can cause severe allergic reactions and permanent scarring if left on for more than 2–3 days. The FDA specifically forbids PPD to be used for this purpose and may prosecute those who produce black henna. Artists who injure clients with black henna in the U.S. may be sued for damages.
The name arose from imports of plant-based hair dyes into the West in the late 19th century. Partly fermented, dried indigo was called black henna because it could be combined with henna to dye hair black. This gave rise to the belief that there was such a thing as black henna which could dye skin black. Indigo will not dye skin black. Pictures of indigenous people with black body art (either alkalized henna or from some other source) also fed the belief that there was such a thing as black henna.
In the 1990s, henna artists in Africa, India, Bali, the Arabian Peninsula, and the West began to experiment with PPD-based black hair dye, applying it as a thick paste as they would apply henna, in an effort to find something that would quickly make jet-black temporary body art. PPD can cause severe allergic reactions, with blistering, intense itching, permanent scarring, and chemical sensitivities. Estimates of allergic reactions range between 3% and 15%. Henna does not cause these injuries. Black henna made with PPD can cause lifelong sensitization to coal tar derivatives while black henna made with gasoline, kerosene, lighter fluid, paint thinner, and benzene has been linked to adult acute leukemia.
The most frequent serious health consequence of having a black henna temporary tattoo is sensitization to hair dye and related chemicals. If a person has had a black henna tattoo and later dyes their hair with chemical hair dye, the allergic reaction may be life-threatening and require hospitalization. Because of the epidemic of PPD allergic reactions, chemical hair dye products now post warnings on the labels: “Temporary black henna tattoos may increase your risk of allergy.
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