An hour of puffs from a hookah packs the same carbon monoxide punch as a pack-a-day cigarette habit. Hookahs have grown in popularity in recent years and Hookah bars have appeared in cities all over the world that allow people to smoke these water pipes. Users inhale tobacco smoke after it bubbles through water, a process that some people think filters toxins from the tobacco.

Hammond and a student, in a study published in the Journal of the American Medical Association, recruited 27 students who smoked water pipes for an hour on three different evenings in April 2006. Another five students did not smoke the hookahs but stayed in the room with those who did. The participants abstained from water pipe smoking for 84 hours before taking part in the study; the bowls of their water pipes were filled with water and 10 grams of Al Fakher muassal tobacco, and then heated with charcoal. Researchers monitored carbon monoxide in the breath of the participants both before and after the experiment using a machine designed to detect if people are smokers. The exhaled carbon monoxide in participants was an average of 42 parts per million, higher than that reported in cigarette smokers (17 parts per million). The study also found that carbon monoxide levels grew in the room where the subjects smoked hookahs and might reach environmentally unhealthy levels, as determined by the federal government, during longer sessions.

Smoking a water pipe for 45 minutes produces 36 times more tar than smoking a cigarette for five minutes.