Hookah tobacco, commonly called shisha, is mostly not tobacco. A typical formula is about 60% glycerol (a thick, sweet liquid used as a moistening agent), 20% tobacco leaf, 10% sugar syrup, and 10% propylene glycol. Flavoring chemicals, from vanilla and fruit esters to mint compounds, round out the mix. But what sits in the bowl is only part of the story. The charcoal burning on top and the chemical reactions triggered by heat introduce a long list of toxic compounds into every puff.
What’s in the Bowl
Shisha looks and feels like a sticky, wet paste, and that’s because tobacco makes up less than 30% of the product by weight, sometimes less than 20%. The bulk of the mixture is glycerol, which typically accounts for 30% to 60% of the total weight. Glycerol serves as a humectant, keeping the tobacco moist and producing the thick, visible clouds hookah is known for. Propylene glycol plays a similar role.
Sugar syrup, usually 5% to 10% of the product, binds the tobacco particles together so they don’t crumble when packed into the bowl. When manufacturers want a milder product with lower nicotine concentration, they add more sugar to dilute the tobacco further, bringing nicotine content down to roughly 0.1% of the total weight.
Then there are the flavorings. The most common flavoring chemicals include vanillin and ethyl vanillin (dessert and vanilla profiles), menthol (mint), ethyl butyrate and isoamyl acetate (fruity notes), and dihydrocoumarin (spice). Fruity esters are either the most or second most abundant class of flavoring compounds across all flavored products. These chemicals are considered safe to eat, but heating them is a different matter entirely.
What the Charcoal Adds
Charcoal is the heat source that sits on top of the bowl, separated by a layer of foil or a heat management device. It doesn’t just warm the shisha. It combusts and contributes its own toxic output directly into the smoke you inhale. Carbon monoxide is the biggest concern. Quick-light charcoal briquettes, the kind you ignite with a lighter, produce an average of 3,728 parts per million of carbon monoxide over a 90-minute session. Natural coconut or wood charcoal produces roughly half that, around 1,730 ppm, but that’s still substantial. The high carbon monoxide output from quick-light charcoal has been linked to a rise in hospital admissions for carbon monoxide poisoning.
Charcoal is also the primary source of polycyclic aromatic hydrocarbons (cancer-causing compounds formed by incomplete combustion) in hookah smoke. This matters because it means even tobacco-free herbal hookah products carry similar risks from these particular toxins.
What Forms When Everything Heats Up
Heat transforms the ingredients in the bowl into a cocktail of compounds that weren’t there before you lit the charcoal. Glycerol and propylene glycol begin breaking down at temperatures below 200°C (392°F), producing formaldehyde, acetaldehyde, acrolein, and acetone. These are toxic carbonyl compounds, and the amount released depends on the ratio of glycerol to propylene glycol in the product.
The sugar syrup caramelizes and decomposes, generating volatile aldehydes. Flavoring chemicals break down too. Terpenes (found in fruity and citrus flavors) can degrade into formaldehyde and isoprene. Esters may form harmful carboxylic acids at elevated temperatures. Furfural, a compound derived from heated sugars, causes pulmonary irritation when inhaled.
Some specific flavorings raise particular concerns. Cinnamaldehyde, the compound that gives cinnamon its flavor, is directly toxic to cells and has shown harmful effects on human embryonic stem cells at low concentrations. Diacetyl, a buttery flavoring compound detected in some shisha products, is the same chemical responsible for “popcorn lung” in factory workers exposed to it. Ethyl vanillin, common in dessert and grape flavors, has proven toxic to human bronchial cells in lab studies. Research has also found that adding apple flavoring to shisha increased cardiovascular dysfunction, oxidative stress, and heart inflammation compared to unflavored products.
The Full Toxic Profile of Hookah Smoke
Mainstream hookah smoke, the smoke you directly inhale through the hose, contains nicotine, cancer-causing nitrosamines, aromatic amines, polycyclic aromatic hydrocarbons, benzene, phenols, furans, carbon monoxide, nitric oxide, and heavy metals. For every 100 puffs during a hookah session, smokers ingest higher amounts of arsenic, chromium, and lead than from a single cigarette. Cadmium, nickel, and lead in the smoke increase cancer risk. Even in best-case scenarios, risk assessments have found that lead and copper levels in flavored tobacco products pose a health concern.
How Hookah Compares to Cigarettes
A single hookah session delivers dramatically more smoke than a cigarette. Pooled estimates put the smoke volume from one hookah bowl at about 74 liters, compared to 0.6 liters from a single cigarette. That’s roughly 125 times more smoke by volume. Tar delivery follows a similar pattern: around 619 milligrams from a hookah session versus 24.5 milligrams from a cigarette. Carbon monoxide intake averages 192 milligrams per session, compared to about 18 milligrams from one cigarette.
Nicotine delivery from a single hookah bowl averages about 4.1 milligrams, with one study measuring 2.94 milligrams from a 10-gram bowl of shisha. A single cigarette delivers roughly 0.88 to 1.8 milligrams. Daily hookah use produces nicotine absorption equivalent to smoking about 10 cigarettes per day. Even a single hookah session for someone who doesn’t smoke daily delivers nicotine equivalent to about two cigarettes.
Does the Water Filter Anything Out?
The water in the base does filter some compounds, but far less than most people assume. Flavoring chemicals are reduced by a factor of roughly 3 to 10, depending on the compound. Benzaldehyde (a cherry and almond flavoring) sees the greatest reduction, about tenfold. Vanillin is reduced about fourfold. Nicotine filtration is modest, reduced by a factor of only 1.4 to 3.1 depending on the flavor blend.
Water solubility doesn’t explain the filtration very well. Nicotine is completely miscible in water yet still passes through in significant quantities. The flavoring compounds have limited water solubility but are still partially captured. The mechanism likely has more to do with how the smoke physically interacts with the water surface than with chemical dissolution. Regardless, the water does not meaningfully reduce carbon monoxide, polycyclic aromatic hydrocarbons, or most of the toxic gases in the smoke.
Herbal and Tobacco-Free Shisha
Tobacco-free hookah products, typically made from sugar cane fiber or tea leaves sweetened and flavored to mimic traditional shisha, eliminate nicotine from the equation. But that’s about all they eliminate. A crossover study comparing tobacco-based and sugar cane-based hookah products found no statistically significant difference in the levels of carbon monoxide, nitric oxide, volatile aldehydes, tar, or polycyclic aromatic hydrocarbons between the two. The smoke from both contained nearly equal amounts of toxicants linked to cancer, cardiovascular disease, and lung disease.
This result makes sense when you consider where most of the toxins originate. Carbon monoxide and polycyclic aromatic hydrocarbons come primarily from the charcoal, not the tobacco. Volatile aldehydes form when sugars and glycerol break down under heat. Since herbal products still use glycerol, sugar syrup, and charcoal, they generate the same harmful byproducts. The only compound they reliably lack is nicotine.