Your conclusion is correct, avoid PPD ‘black henna’ tattoos. But the problem isn’t technically a burn, it potentially causes allergic contact dermatitis, just like poison ivy or oak, and once sensitized you remain sensitized to that for life. It doesn’t sensitize as easily as poison ivy, few things do, but PPD is one of the most common sensitizers. If the liquid dye gets on the scalp when coloring hair it can sensitize folks but happily once it’s dry and has done its hair coloring task it no longer reacts. Or else the patients I’ve seen who became allergic to hair dyes would have had to shave their scalps to end their itchy rashes. Henna without PPD gives a shorter lasting ‘temporary tattoo.’ Henna, alone, on hair gives Lucille Ball colored hair. Lucy was naturally a blond as shown in her older movies. Allergic reactions to henna alone are possible, but fairly rare.
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