More and more people around the world are switching to electronic cigarettes - known as 'e-cigarettes' - as a substitute for conventional cigarettes. An estimated 2.6 million people in the UK alone are using one of the nearly 500 brands of e-cigarettes available from high street shops, petrol stations and via the internet. And yet little is known about the health risks associated with e-cigarettes, which have been in use since they were invented 13 years ago in China.

The authors of a new article published in the latest issue of The Journal of Laryngology & Otology (JLO) point out that - although e-cigarettes are often marketed as using only vapour and nicotine without the carcinogens such as tar found in conventional cigarettes - there have been various chemical compounds found in e-cigarettes that are "either already known to be carcinogens or may well prove to be carcinogenic in the future". And since e-cigarettes are currently not regulated, users cannot be certain about which chemicals are found within each product.

In this article, the three co-authors - who are all experts in the field of respiratory medicine and otolaryngology from hospitals in England - set out to examine the regulations, trends and health risks associated with e-cigarettes, as well as summarising the evidence about the use of e-cigarettes in smoking cessation.

What they found is that many of the elements identified in e-cigarette aerosols are known to cause respiratory distress and disease. One 2013 study found, for example, that tin, silver, iron, nickel, aluminium and silicate particles have all been found in e-cigarette aerosols. The same study also found that the concentrations of nine out of eleven elements in e-cigarette aerosols were higher than or equal to the corresponding concentrations found in conventional cigarette smoke.

In addition, the US Food and Drug Administration (FDA) found diethylene glycol - a toxic chemical that can cause death - in one e-cigarette. And the authors point out that significant amounts of nicotine have also been found in some refill fluids or vapours for e-cigarettes, in spite of some manufacturers' claims that their products are nicotine free.

A more recent 2015 study has confirmed that e-cigarettes contain toxic compounds, such as formaldehyde, nitrosamines and nickel, although these were in much lower concentrations than found in conventional cigarettes.

The authors highlight short-term evidence including eye and respiratory irritation caused by exposure to propylene glycol found in e-cigarettes, as well as troubling reports in the media about e-cigarettes being potential fire and explosive hazards, with claims that they have been responsible for up to 100 fires over the past two years.

In addition, the authors report that there is limited evidence to prove whether e-cigarettes are an effective method for stopping tobacco smoking. Although several trials suggest that e-cigarettes may be beneficial to some smokers who are looking to quit or reduce smoking, the authors conclude that there is currently not enough long-term data available on the outcomes of using e-cigarettes as smoking cessation devices. At the moment, no e-cigarettes have been approved for smoking cessation purposes by governmental authorities, according to the authors. However, as a result of the European Commission's Tobacco Products Directive issued in 2014, the Medicines and Healthcare Products Regulatory Agency (MHRA) in the UK is currently considering regulation of e-cigarettes and other nicotine-containing products.

In the meantime, the authors recommend that professionals should not be advocating the use of e-cigarettes as a smoking cessation tool.

"Regulation of e-cigarettes is necessary to establish a scientific basis on which to judge the effects of their use," they conclude. In addition, they recommend that adequate research is needed on the long-term health effects of e-cigarettes, "firstly so that the public has current and reliable information as to the potential risks and benefits and secondly so that the health of the public is protected."

Article: E-cigarettes in ENT: what do we need to know?, Nicola Stobbs, Dr Aoife Lillis and Professor Nirmal Kumar, The Journal of Laryngology & Otology, doi: 10.1017/S002221511600102X, published online 19 April 2016.