Hookahs, which many people perceive as a less dangerous way of using tobacco than smoking cigarettes, can cause carbon monoxide poisoning, health experts say.

The health effects of hookahs, or water pipes, have not been studied as rigorously as cigarettes, but the risks are becoming clearer as the pipes grow in popularity in the United States, Thomas Eissenberg of Virginia Commonwealth University, who has studied hookahs extensively, told The Courier-Journal.

Hookah bars feature water pipes that are used to smoke a blend of tobacco, molasses and fruit called shisha. Researchers say that contrary to the belief of many hookah smokers, the water in the pipe does not filter all the harmful chemicals in tobacco smoke. The World Health Organization (WHO) noted in a report that the smoke inhaled in a typical one-hour hookah session can equal 100 cigarettes or more. The WHO report also stated that even after it has been passed through water, the tobacco smoke in a hookah pipe contains high levels of cancer-causing chemicals.

Henry Spiller, Director of the Kentucky Regional Poison Center, told the newspaper that he has seen hookah users with significant carbon monoxide poisoning. He noted that regular hookah users may develop long-term health problems from increased carbon monoxide levels, including neurological damage. In severe cases, carbon monoxide poisoning can lead to a coma or death.