The so-called cinnamon challenge—a dare to swallow a spoonful of cinnamon without water—has gone viral and beyond. Though the challenge has been around for years, its popularity has spiked recently, to the amusement—or puzzlement—of many.

Some 30,000 videos tagged "cinnamon challenge" have been uploaded on to YouTube. The most popular, with almost nine million views, was uploaded last month; it shows a woman with big earrings slurping a pile of brown powder from a soup ladle and immediately, dramatically, spitting it out. A fit of coughing follows.

The difficulty is that the spice doesn't break down very fast and can get stuck in the throat, causing gagging and even vomiting. Doctors say this can be dangerous because the cinnamon can prevent air from reaching the lungs. "It is an obvious choking hazard and there is a risk of inhaling the dust. This certainly is not advisable," says a spokesman from the Food and Drug Administration.

Dr. Jeffrey Cain, president-elect for the American Academy of Family Physicians, says the cinnamon itself isn't dangerous—but inflammation of the lungs is a real possibility. That, and being laughed at, he says.

As a result, schools from Alabama to Guam are warning parents and staff about the potential dangers of swallowing so much cinnamon at once. "The kids all know about this from the Internet but the parents have no idea," says Arthur Williams, principal at Huron High School in Ann Arbor, Mich., who emailed parents after a student was recently hospitalized for 4½ days because of lung trouble after trying the challenge.

Pottstown Middle School in Pottstown, Pa., which has had three reported incidents of students taking the cinnamon challenge on campus since January, caught a student trying to smuggle a vial of cinnamon into school in a pair of boots. The school subsequently put a ban "open-top boots," also intended to stop cellphone smuggling.