The danger: Stroke

The source: Shape

The details: "I had a large blood clot in my left lung -- a pulmonary embolism -- which had already damaged part of my lung....But that was the least of my worries. There was a risk it could move to my heart or brain where it would surely kill me."

The fine print "Doctors told me they would test for a gene I had never heard of: Factor V Leiden, which causes those that carry it to be predisposed to life-threatening blood clots....It's estimated that about four to seven percent of the population [has it]."

The bottom line: Welp, guess it's back to the pull-out method.

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.