'Black Henna' Is a Misnomer
Technically speaking, there's no such thing as 'black henna'. Henna, the crushed leaves of the shrub Lawsonia inermis, produces a vivid red-orange dye when liquid is added. No species of henna produces any other colour, although compound henna—a mixture of low-quality henna and other ingredients – is sometimes sold in various colours for dyeing hair.
A few stores sell indigo – another plant-based hair dye which produces a blue-black colour – under the name of black henna. While not henna, indigo is still a safe, natural dye and can be used to effectively dye hair black (it is ineffective for mehndi). However, most 'black henna' on the market is actually para-phenylendiamine (PPD), a harmful chemical.
Uses of 'Black Henna'
Para-phenylendiamine (PPD) is sold both as a hair dye and a temporary tattoo ink. It is in the latter capacity that is falsely labelled 'black henna'. Some temporary tattoo artists, especially at holiday destinations, use PPD dyes to create 'black henna tattoos'. As it takes a few hours for the harmful effects of PPD to develop, such artists often escape legal repercussions.
Harmful Effects of Para-Phenylendiamine (PPD)
PPD has been reported to cause numerous health issues, from the mild to the deadly. Common initial reactions include itching, hives, swelling and redness. Over the next few days the symptoms may worsen to include severe swelling leading to respiratory obstruction, renal failure, muscle pain, hair loss, collapse and even death. Longer-term effects include sensitization and permanent scarring. Sufferers often require the use of steroids for long-term treatment.
PPD is mutagenic and has been shown to be carcinogenic in animals.
Allergies Resulting From Use of 'Black Henna'
PPD is a sensitizer. If an allergic reaction is experienced it can trigger further allergies to substances including hair dye, ink, some sunscreens and several drugs.
Legality of Dyes Containing PPD
Para-phenylendiamine for use on the skin has been outlawed in several countries such as Sweden, Germany, France and Canada. Its use in hair dyes is limited to extremely low concentrations, and the dyes must contain safety warnings. The FDA also notes that PPD is approved only for hair dyes and should not be used on the skin.
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