The FDA has a new warning about the dangers of temporary henna tattoos.
The agency's director says people are reporting bad reactions to the ink.
Symptoms include redness, blisters and lesions.
Dermatologists say the tattoos themselves aren't always the problem, but people add things to the ink to make it darker, or show up faster.
They call it "black henna."
Doctors say it can cause allergic reactions in anyone who has problems with hair dye.
FDA officials say "black henna" is mostly used in temporary tattoo booths on beaches and boardwalks.
They recommend anyone thinking about getting one of the tattoos ask specifically about the ink.