Hookah bars are a relaxed gathering place for customers to socialize as they smoke tobacco through water pipes. It’s a hot trend among young adults. Nearly one in five US students smoked hookah in the last year, according to a study published in the journal Pediatrics. About 10 businesses sell hookah within a five-mile radius of the University of Texas at Dallas.

But hookah, which comes with few warning labels or health notices, can be more dangerous than smoking cigarettes. A study funded by the National Institutes of Health notes that a single hookah session delivers 1.7 times the nicotine, 6.5 times the carbon monoxide and 46.4 times the tar of a single cigarette.

“There is no reason to believe that a water pipe is less dangerous than a cigarette,” says Dr Thomas Eissenberg, a Virginia Commonwealth University professor who has conducted numerous studies on water pipe smoking. “In fact, depending on some of the toxins, there is reason to believe it is more dangerous.”