There's plenty of scientific evidence showing regularly using a hookah is unhealthy, but now a new study says even those who smoke with a hookah occasionally are putting themselves at risk. NY1's Erin Billups filed the following report.

The Centers for Disease Control says there's been a steady rise in hookah use among high school and college students - many assuming it's less harmful than smoking cigarettes.

"There's this perception among hookah users is that because it's bubbled through water it's probably safer. The question is that true or not," says Dr. Ronald Crystal, Chair, Department of Genetic Medicine at Weill Cornell Medicine.

Crystal studied 40 twenty-somethings in the city - half of them users of hookahs a couple of times a week. His researchers logged how much they coughed and the amount of mucus they produced, and studied cells from their lungs and blood.

"The striking feature was that all of these things were abnormal. Despite the fact that these are young people, they don't smoke all that much, but they had considerable abnormalities," notes Crystal.

One especially troubling finding - the cells of the hookah users were in disarray, similar to cells found in the lungs and blood of cigarette smokers.

"Many of these genes that we see behaving abnormally are genes that we know can lead to disease. So whether or not it will lead to disease in these individuals, we don't know. But the fact is that the person who's walking down the street who's a hookah smoker who thinks they're absolutely fine, in fact at the biologic level they're not," says Crystal.

It's the inhaling of chemicals, including burned charcoal, in hookah smoke that raises the health risk. Only non-tobacco herbal mixtures are supposed to be smoked in city hookah bars, but studies show tobacco sometimes is still mixed in.

The study comes as the City Council is weighing whether to limit even tobacco-free hookah use in some bars and restaurants.

"We're going to have to do more studies, bigger epidemiologic studies - but if I was considering on the City Council for example - should I control some of this? My recommendation would be yes," says Crystal.

Crystal plans to study a larger group of hookah smokers. To be considered, contact the Weill Cornell Medicine department of Genetic Medicine at 646-962-4363.

His research is published in The American Journal of Respiratory and Critical Care Medicine.