The danger: A disfiguring burn and anaphylactic shock

The source: Seventeen

The details: "She went to get it retouched, and after just a few hours, it started to swell ... 'Bits of my skin were coming off. It was just disgusting ... it looked like open flesh.'" The fine print: "The burn was caused by p-paraphenylenediamine, a chemical found in black henna ... a synthetic coal tar dye, not approved by the FDA. It's not often used in the U.S., but it's still something to look out for."

The aftermath: "Mary now has to take major precautions in her daily life, since exposure to this chemical is really dangerous. She can't go out in the sun for at least two years without protection, and she can't dye her hair."

The bottom line: If you want a tattoo, just go for the permanent version. Clearly, a safer choice.