A showing-off stunt that may seem harmless actually isn't, experts warn. The teen craze, called The Cinnamon Challenge, has spread since last year and only sounds like a baking contest. The test involves swallowing a tablespoon of ground cinnamon in a minute or less without water while being videotaped. The result can look funny, but doctors aren't laughing because at least 30 U.S. teens needed medical attention after trying it last year, says an article in the journal Pediatrics.

There also has been a surge in calls to U.S. poison centers as the challenge spreads via more than 51,000 YouTube videos. Cinnamon, made from tree bark, has cellulose fibers that don’t easily break down. Animal research suggests that when cinnamon gets into the lungs, it can cause scarring, says Dr. Steven Lipshultz, one writer of last week's journal article. He's a medical school professor at the University of Miami.

The immediate effects – coughing, choking and burning of the mouth, nose and throat – are temporary in most cases, But it's especially dangerous for some youths and adults. "People with asthma or other respiratory conditions are at greater risk of having this result in shortness of breath and trouble breathing,” according to an alert from the American Association of Poison Control Centers. Dejah Reed, a 16-year-old from Ypsilanti, Mich., was hospitalized last year and now uses an inhaler occasionally – although she didn't have asthma before trying the challenge four times. She started a website urging telling teens to "just say no" to the fad. It's at nocinnamonchallenge.com

Student says: "I was laughing very hard and I coughed it out and I inhaled it into my lungs. I couldn’t breathe." – Dejah Reed, 16, Ypsilanti, Mich.

Doctor says: "Some people are able to swallow the cinnamon without looking like they want to die. Most are not." – Dr. James Hamblin, health editor of The Atlantic magazine

Parents' role: "This is a call to arms to parents and doctors to be aware of things like the cinnamon challenge." – Stephen Pont of the American Academy of Pediatrics, adding that parents should know what children watch online