Hookahs are not safer than cigarettes, the American Heart Association (AHA) has warned. They often contain more toxic chemicals, and their use may harm heart and blood vessels.

In a statement in the journal Circulation, the AHA says that while direct comparisons have some limitations, a single session of hookah use typically results in greater exposure to carbon monoxide than a single cigarette. The reason, in part, is that sessions usually last for half an hour or more.

But even short-term exposure to carbon monoxide in hookahs is toxic and can interfere with exercise capacity.

“Many young people mistakenly believe that smoking tobacco from a hookah is less harmful than cigarette smoking because the tobacco is filtered through water, but there is no scientific evidence that supports that claim,” says Aruni Bhatnagar, chair of the statement writing group.

“However, there is evidence to suggest that hookah smoking is addictive and can lead to the use of other tobacco products such as cigarettes.”

Hookahs, which go by a number of names, are water pipes comprising a head or bowl to hold flavoured tobacco, a base full of water, and a hose that ends with a mouthpiece. Burning charcoal is placed on top of the bowl.

While the tobacco is usually not just tobacco – dried fruit and substances to keep it moist is mixed in – users still inhale large quantities of nasties.

Despite this, the AHA says, hookah tobacco is often colourfully packaged and can be sold in candy and fruit flavours that appeal to younger audiences. The flavours and sweeteners mask the harshness of smoke, making it easier to start and continue smoking hookahs.

In addition, because many people smoke hookahs in lounges and cafes, it is perceived to be a social activity and less habit-forming.

In the US, surveys have estimated that 13.6% of young adults, aged between 18 and 24 years, smoke hookahs, and account for 55% of people who use the devices. Significantly, those who use hookah were found to be more likely to start smoking cigarettes.

A 2018 study in the UK found that smoking hookahs, known as shishas, “plays a central role in social interactions” and that “the known health dangers of shisha are outweighed by its social benefits”.