Popular heated tobacco devices may cause the same damage to lung cells as traditional cigarettes.
Meanwhile, e-cigarettes are also toxic to the cells which protect the lungs, so might not be a safe alternative to smoking, a study suggests.
Both electronic devices, used by thousands of people to quit smoking, are now thought to cause the airway damage seen in people with emphysema, bronchitis and lung cancer.
Australian researchers found they harm the lung cells which protect the airways, just as cigarette smoke does.
Cell damage: Australian researchers found that heated tobacco devices and e-cigarettes harm the lung cells which protect the airways, just as cigarette smoke does
The study looked at the IQOS, a ‘next-generation’ heated tobacco device used by 6.6million people and sold in Britain.
Priced at more than £50 for a starter kit from Amazon, the trendy product heats rather than burns tobacco to produce a similar flavour to cigarettes but lower levels of chemicals.
However it was found to damage human lung cells, changing their structure and triggering an inflammatory response.
Dr Sukhwinder Sohal led the study from the University of Tasmania, looking at cigarettes, e-cigarettes and the IQOS, which is made by tobacco giant Philip Morris International.
He said: ‘Our results suggest that all three are toxic to the cells of our lungs and that these new heated tobacco devices are as harmful as smoking traditional cigarettes.
‘Damage to these two types of lung cells can destroy lung tissue leading to fatal diseases such as chronic obstructive pulmonary disease, lung cancer and pneumonia, and can increase the risk of developing asthma, including in unborn children.
‘So we should not assume that these devices are a safer option.’
Cigarettes, electronic cigarettes and heated tobacco devices all contain nicotine - the addictive substance which gets people hooked.
But e-cigarettes contain a liquid form of nicotine that is heated into vapour to be inhaled, avoiding the harm caused by tobacco smoke.
Heated tobacco products like the IQOS are marketed as being safer than cigarettes because tobacco is not burned, which produces smoke containing many harmful chemicals.
Instead it is heated, producing fewer chemicals and no fire, ash or smoke.
Risk: Cigarette smoke and heated tobacco vapour were highly toxic to the cells both at lower and higher concentrations while e-cigarette vapour was toxic mainly at higher levels
Researchers tested the effects of all three devices on epithelial cells and smooth muscle cells taken from the human airways.
In healthy lungs, epithelial cells act as the first line of defence to any foreign particles entering the airway while smooth muscle cells maintain its structure.
When they are damaged, they cause the scarring and reshaping of the airway seen in lung patients.
The study found the electronic devices caused this damage, including changes to cell structure and function, as well as a ‘cry for help’ inflammatory response.
That inflammatory response was as strong for the heated tobacco device as when the lung cells were exposed to smoke from Marlboro Red cigarettes.