Dangerous chemicals added to henna tattoos to make them stain the skin a pure black can cause allergic reactions and permanent scarring in as much as 1.5% of the population, or 1 in every 75 people.
Natural henna tattoos are created from the Lawsonia Inermis shrub. They leave a brown, red, or orange stain on skin. Any other color of henna—including green, blue, purple, and black—has had chemicals added to it. Some of these chemicals are harmless, but black henna typically contains para-plenylenedemine (PPD), which can be extremely dangerous.
PPD is most commonly found in hair dye. In the US, over 99% of all hair dyes include a small percentage of PPD, but many European countries have banned any use of the dangerous chemical. Because of PPD’s volatile attributes, no more than 6% of a hair dye product can be PPD and people handling hair dye containing PPD are cautioned to always use gloves and avoid exposure to skin.