Previous studies found that hookah smoking, also known as waterpipe smoking, is more dangerous than cigarette smoking. But just how dangerous is it? A recent study shows that one hookah session gives the smoker 25 times the tar of a single cigarette.

Researchers from the University of Pittsburgh Schools of the Health Sciences conducted a review of previous literature regarding hookah and cigarette smoking. Starting with 542 relevant articles, they identified 17 that provide estimates of the toxicants that hookah and cigarette smokers inhale.

The researchers found out that aside from delivering 25 times the tar of a single cigarette, hookah smoking also gives 125 times the smoke, 10 times the carbon monoxide and 2.5 times the nicotine of a cigarette.

"Our results show that hookah tobacco smoking poses real health concerns and that it should be monitored more closely than it is currently," lead author Dr. Brian A. Primack said in a press release.

He said that hookah smoking is not as closely monitored as other forms of substance abuse. For example, it was excluded in the 2015 Youth Risk Behavior Surveillance Survey System, which looked at the use of cigarettes, tobacco, electronic cigarettes and others.

Primack said comparing hookah smoking and cigarette smoking is not an easy thing. For one thing, the frequency of smoking varies between cigarette smokers and hookah smokers.

"It's not a perfect comparison because people smoke cigarettes and hookahs in very different ways," he said. "We had to conduct the analysis this way -comparing a single hookah session to a single cigarette - because that's the way the underlying studies tend to report findings."

Thus, the estimated figures they extracted did not identify which of the two is worse.

"But what they do suggest is that hookah smokers are exposed to a lot more toxicants than they probably realize. After we have more fine-grained data about usage frequencies and patterns, we will be able to combine those data with these findings and get a better sense of relative overall toxicant load," Primack said.

Waterpipe smoking has several negative effects on health. It can cause lung, oral and bladder cancers, heart disease and clogged arteries. The juices from hookah increases the likelihood of developing oral cancer. Additionally, the charcoal used for heating the tobacco produces metals, carbon monoxide and other toxic substances, according to the Centers for Disease Control and Prevention.

The study will be published in the January/February 2016 issue of Public Health Reports.