Spring break is around the corner, as is summer vacation, which means you may be thinking of getting a temporary tattoo. After all, it’s temporary, so it’s harmless, right?

Not so fast. The Food and Drug Administration has issued a new health warning, asserting that temporary tattoos may pose some health risks.

Temporary tattoos can last anywhere from three days to several weeks. Although they aren’t injected into the skin, they do come with some risks, said Dr. Linda Katz, director of the FDA’s Office of Cosmetics and Colors.

Katz said consumers are still at risk for allergic reactions, which can be severe and can last even longer than the tattoo itself.

MedWatch, the FDA’s safety information and adverse event reporting program, has received many reports of serious, long-lasting reactions that consumers did not expect when they first got the temporary tattoo. Problems include redness, blisters, raised red weeping lesions, loss of skin pigmentation, increased sensitivity to sunlight and even permanent scarring.

The FDA said some consumers had to seek medical attention after getting one of the tattoos, including trips to the emergency room. Sometimes these trips occurred right after the tattoo was placed on the skin, and sometimes they occurred weeks after the event.

Usually, temporary tattoos are done using henna – a reddish-brown coloring that derives from a flowering plant. Modern-day henna is called “black henna” and is often used in place of traditional henna. Inks marketed as black henna may be mixed with several other ingredients – or it could just be hair dye by itself. The FDA said adding other ingredients to the henna makes the tattoo last longer and look darker.

The extra ingredient in black henna is often coal-tar hair dye, which contains p-phenylenediamine (PPD), an ingredient that can cause dangerous skin reactions in some people, according to the FDA. The tattoo artist may use PPD-containing hair dye by itself, but either way, it’s dangerous and hard to tell which product is used.

Black henna tattoos may be sold at beaches, boardwalks or specialty shops. Some states have jurisdiction over professional cosmetology practices, but these vary by each state. It’s feasible that in whichever state you receive the tattoo, there is no licensed board checking to see if the artist is following safe and clean practices.

One 5-year-old girl experienced severe reddening on her arm two weeks after receiving a black henna temporary tattoo, while a 17-year-old experienced redness and itching that later blistered and filled with fluid.

If you have an allergic reaction to a temporary tattoo, please contact the FDA’s MedWatch, or call 1-800-FDA-1088.

Click for more info from the FDA.