Hookah smoking sends people to the ER with carbon monoxide poisoning - even outdoors

How dangerous can a single hookah session be? Dangerous enough to cause you to collapse after leaving the venue, even if you smoked for less than an hour, even if you were sitting outside.

A systematic review published in the JMA Journal compiled 68 documented cases of acute carbon monoxide poisoning linked to waterpipe tobacco smoking - also known as shisha, hookah, or narghile - and found that the circumstances under which poisoning occurs are far broader than most users realize.

The charcoal problem

Waterpipe smoking works by heating flavored tobacco with burning charcoal, then drawing the smoke through water before inhalation. The water cools the smoke and filters some particulates, which gives users a false sense of safety. But the charcoal is the real hazard. Incomplete combustion of charcoal generates carbon monoxide (CO), a colorless, odorless gas that binds to hemoglobin roughly 250 times more readily than oxygen does.

In Tokyo alone, within the jurisdiction of the Third Fire District Headquarters covering three southwestern wards, emergency services recorded roughly one case of acute CO poisoning from waterpipe smoking every month between January 2018 and June 2023. Most victims were young adults.

What 68 cases reveal

The research team at the University of Tsukuba, led by Professor Isao Muraki, searched six academic databases for case reports and case series of CO poisoning associated with waterpipe use worldwide. The 68 cases broke down as follows:

• 41 involved individual active smokers
• 23 were clustered incidents, with up to 12 people poisoned simultaneously in indoor settings
• 2 involved nonsmoking bystanders
• 2 involved employees working in waterpipe cafes

The most common symptom was syncope - fainting - reported in 53% of cases. Headache followed at 50%, lethargy at 44%, nausea or vomiting at 38%, and weakness at 15%. Some patients presented with tremors, visual disturbances, or seizures.

Delayed, brief, and outdoor - none are safe

Three findings stand out. First, roughly one-quarter of patients developed symptoms only after they had already left the smoking venue. CO binds tightly to hemoglobin and clears slowly; a person can feel fine while smoking and deteriorate on the walk home or in the car.

Second, about one-fifth of cases occurred after less than one hour of waterpipe use. The notion that a quick session is harmless does not hold up.

Third, another one-fifth of cases happened during outdoor smoking. Open air dilutes CO concentrations, but evidently not enough to prevent poisoning in all circumstances - particularly when multiple charcoal units are burning in proximity or wind conditions are unfavorable.

The chronic toll: polycythemia

Beyond acute poisoning, the review identified 13 cases of polycythemia - a condition marked by persistently elevated hemoglobin levels and increased red blood cell counts. The body, starved of oxygen by chronic CO exposure, ramps up red blood cell production as a compensatory mechanism. Twelve of the 13 polycythemia patients reported daily waterpipe use. The condition raises the risk of blood clots, stroke, and other cardiovascular complications.

Indoor clusters are the worst-case scenario

Clustered poisoning events - multiple people sickened at once - were strongly associated with enclosed indoor environments. In one case, 12 individuals were poisoned simultaneously. These scenarios represent a particular public health concern because waterpipe lounges and cafes, by design, concentrate multiple charcoal-burning devices in a single space. Without CO monitors or adequate ventilation, toxic gas levels can build rapidly and affect everyone in the room, including staff and nonsmoking patrons.

What this means for regulation and awareness

The researchers argue that current awareness among waterpipe users and venue operators is inadequate. Many users equate the water filtration with safety, and many venues lack basic CO monitoring equipment. The study calls for mandatory CO detectors in indoor waterpipe venues, improved ventilation standards, and public health messaging that specifically addresses the CO risk - distinct from the tar and nicotine concerns that dominate tobacco messaging.

The review has limitations typical of case report analyses: it captures only cases severe enough to generate a medical publication, likely underrepresenting the true incidence. Mild CO poisoning from hookah use probably goes unrecognized and unreported. The study also cannot establish incidence rates since the denominator - total waterpipe sessions worldwide - is unknown.