“Black henna” is the name given to an artificial product created by the addition of paraphenylenediamine (PPD) to natural henna to create a black stain. PPD is traditionally used in black hair dye but is a sensitizer, which means that it is something that the body is naturally allergic to or can become allergic to. Black henna can cause severe reactions that can take from 5–15 days to appear, which can cause permanent scarring and may even be life threatening. Reactions to black henna frequently necessitate immediate medical attention from a doctor or allergist.
While there are many vareities of the henna plant which create many different colours and hues on the skin, there is no variety of henna that appears ‘black’ on the skin. If a henna artist is advertising ‘black henna’ DO NOT USE THEM. Only the addition of PPD can make henna appear black, and PPD is very dangerous.
Please read the Health Canada advisory below, and follow the CBC link for additional information.
Advisory
2003-66 August 11, 2003 For immediate release
Health Canada alerts Canadians not to use “black henna” temporary tattoo ink and paste containing PPD
OTTAWA – Health Canada is advising Canadians that the use of the ingredient para-phenylenediamine (PPD) in “black henna” temporary tattoo ink and paste is unsafe. Allergic reactions to PPD include red skin rashes, contact dermatitis, itching, blisters, open sores, scarring and other potentially harmful effects. Allergic reactions to PPD may also lead to sensitivity to other products such as hair dye, sun block and some types of black clothing.
PPD is an acceptable ingredient in hair dyes that, when used correctly, do not come into contact with skin for prolonged periods of time. The use of PPD in cosmetics applied to the skin for prolonged periods of time poses a risk to the health and safety of the user. As such, “black henna” temporary tattoo ink and paste containing PPD is not considered safe.
Under Section 16 of the Food and Drugs Act, no person shall sell cosmetics that contain substances that may cause injury to the health of the user when the cosmetic is used according to the directions on the label or accompanying the cosmetic. Cosmetics containing PPD that are applied directly to the skin are not to be sold in Canada. This includes “black henna” temporary tattoos containing PPD, which are often sold and applied by artisans at markets, fairs and amusement parks.
Before receiving a temporary tattoo, ask the vendor to confirm that PPD is not being used in the ink or paste. Health Canada permits the use of natural henna and other safe dyes in cosmetics.
Here are some things to look for if you suspect that PPD is being used in “black henna” tattoo ink or paste: PPD in “black henna” is used for its long-lasting properties and intense black colour. If the formula and resulting tattoo are jet black, the ink or paste may contain PPD; If the tattoo is to be removed within an hour, the ink or paste may contain PPD; PPD stains typically last one to three weeks, without fading; and, PPD-black henna mixes usually have very little or no scent.

Please contact your nearest Health Canada Product Safety Office if you suspect that PPD is being used by a local vendor. http://www.hc-sc.gc.ca/ahc-asc/media/advisories-avis/2003/2003_66_e.html
Link to CBC Consumer article on the dangers of BLACK HENNA http://www.cbc.ca/consumers/market/files/health/henna/