Spring Break Alert: 'Black' Henna Tattoos May Not Be Safe

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A popular spring break souvenir may have more staying power than you'd like if it contains the chemical p-phenylenediamine, or PPD.

A henna tattoo looks like a fun beach souvenir — until you break out in a rash and blisters.

The dyes used for the popular temporary tattoos aren't always natural or safe, the Food and Drug Administration warned today. "Black henna" used to make the intricate designs darker often doesn't come from a plant, but from a harsh chemical that causes allergic reactions.

The bad actor is p-phenylenediamine (PPD), a chemical derived from coal tar that can cause skin allergies. It's sold as hair dye, and sometimes people doing henna tattoos use it because it dries faster and has a darker hue than the brownish red of traditional henna.

But PPD isn't supposed to be used on the skin. And the FDA says it has received reports that it is, including a 5-year-old girl with blisters on her forearm two weeks after getting a "henna" tattoo, and a teenager whose back was blistered and raw.