It is growing in popularity but some experts say a single shisha session is the same as smoking 200 cigarettes

For Jawad Rezavi, 26, smoking shisha is the perfect way to unwind in an evening. "After a long day, I'll go to a shisha lounge. It relaxes me. In the same way that some people will enjoy a glass of red wine or need a cigarette to keep going while they're working, I like to enjoy my shisha. If I don't do it, it feels like I'm missing something."

Shisha, the origins of which are disputed (some say India, others Persia or Turkey) is a glass-bottomed water pipe in which fruit-flavoured tobacco is covered with foil and roasted with charcoal. The tobacco smoke passes through a water chamber and is inhaled deeply and slowly; the fruit-flavoured tobacco tastes smooth and smells sweet, enthusiasts say, making it an enjoyable and unrushed experience.

Rezavi, a student from London, tried his first shisha when he was 16. He began smoking regularly five years ago and helped his father establish a shisha cafe. The cafe closed down after the smoking ban came into effect in 2007, but Rezavi still smokes six times a week, either at home or at one of his favourite shisha bars with friends. "It's part of my routine. It's just nice to have it bubbling in the background when I'm studying."

And he's not alone. Usually shared between friends shisha is now associated with Middle Eastern cafe culture, but has become increasingly popular in the UK in recent years with cafes popping up in cities across the country. It's a phenomenon that has worried primary care trusts (PCTs) across the UK, which think that, unlike cigarette smokers, shisha users are unaware of the health risks.

Earlier this year, Leicester PCT's Stop Smoking service said it had seen an alarming rise in the number of teenagers in the city smoking shisha. And this summer, Birmingham's three PCTs will launch a city-wide tobacco control strategy, which includes increasing the awareness of shisha smoking. Meanwhile, the Niche Tobacco Advisory Group (NTAG) for North England recently introduced an educational campaign on shisha smoking.

Dr Khalid Anis, chairman of NTAG in Manchester, says: "There's a misconception that shisha is not as bad for you as cigarettes, because the tobacco is flavoured and passes through water first. But the carcinogens and nicotine are still there. So a regular shisha smoker can expect to be at risk to the similar health problems that cigarette smokers face, whether that's respiratory, heart disease or cancer. As with any other tobacco product, I expect regular shisha smokers will find it addictive, to the point that they may need it every day."

According to research carried out by the World Health Organisation (WHO), the volume of smoke inhaled in an hour-long shisha session is estimated to be the equivalent of smoking between 100 and 200 cigarettes. The estimated findings go on to show that, on average, a smoker will inhale half a litre of smoke per cigarette, while a shisha smoker can take in anything from just under a sixth of a litre to a litre of smoke per inhale.

But a niche tobacco expert from a London local authority suggests the WHO findings are "alarmist", pointing out that there's not yet been enough research into the long-term effects of shisha smoking. Dr Kamal Chaouachi, a tobacco expert who teaches at Paris IX University and has researched shisha for 15 years, says comparing shisha with cigarettes "amounts to comparing oranges to apples".

According to Chaouachi, studies led by independent researchers at the Royal University of Saudi Arabia have shown that shisha smoke is 30 times less concentrated in chemicals than cigarette smoke, contradicting the WHO's warnings. "It is ludicrous and anti-scientific to claim that hookah or shisha smoke is 200 times more toxic than cigarette smoke," he says. "While about 5,000 chemicals have been identified so far in cigarette smoke, chemists and pharmacologists from Saudi Arabia only found 142 chemicals in shisha smoke. Also, a medical team in Pakistan found that shisha smoke can be much less carcinogenic and radioactive than cigarette smoke."

In March, the BBC published a news story claiming that GPs in Leicester "are seeing an increase in teenagers with health problems linked to shisha pipe smoking". But Leicester PCT now says the story was erroneous; while it maintains the number of teenagers in the city smoking shisha is on the rise, it says GPs have not confirmed an increase in treating patients with health problems caused directly by shisha.

So, with all the conflicting evidence, are the health concerns around shisha just a load of hot air? "The research on shisha is admittedly limited," concedes Anis. "But I have to concur with the WHO. If you watch the way people smoke shisha, they take deliberate, deep breaths before exhaling so there is a lot of smoke being inhaled."

Rezavi is unconvinced by the arguments. "Sure, inhaling tobacco smoke, whether it's from shisha or cigarettes, is never going to be good for you," he says. "I know that, but at the end of the day it's just something I enjoy."