The culprit behind reactions from the body art is the ingredient para-phenylen­ediamine (PPD), used in coal-tar hair dye that effectively blackens henna. PPD can leave behind blisters and burns to the skin that can scar, along with a sensitivity to the ingredient that could flare up after future use of hair dye.

"Black henna is well known to cause skin reactions and should be treated with caution, particularly in children. ... What might seem like pretty body art can quickly turn nasty with horrific blistering, permanent scars and even in the most severe cases life-threatening allergic reactions," said Anjali Mahto, consultant dermatologist and spokesperson, British Skin Foundation.
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