Tattoos are no longer an act of outrageous rebellion. Fully 32% of U.S. adults have one, and that number rises to 40% of people 18-34 years old.

But it turns out all that ink is lighting up more than their appearance.

It can trigger an increased risk of heart failure, as well as allergic dermatitis, according to a study in the Journal of the American Academy of Dermatology.

Ten pigments, including black 11, blue 15, green 7, blue 15, orange 34, red 101, red 122, red 181, red 210, yellow 42, yellow 65, and solvent yellow 33 are the troublemakers. According to the Food and Drug Administration, some inks contain pigments used in printer toner and car paint — no wonder they haven't approved any for tattooing.

Allergic dermatitis is an immune reaction to a skin irritant that causes painful, red, itchy bumps and rashes. While allergy pills and cortisone creams may ease the reaction, they won't go away until the irritant (in this case, the ink) goes away.

Getting your tattoo removed isn't easy.

Still want to decorate your skin? Consider a temporary henna tattoo — but avoid black henna, which also can trigger serious allergic reactions.

The Cleveland Clinic says to make sure fresh, sterilized needles are being used and ask what kind of ink is going on your skin. If the henna mixture smells like chemicals or gas, that's black henna. Turn around and walk out.