New York, Dec 5 (IANS): Researchers have found that the vapours which are produced after e-liquid flavourings are heated inside e-cigarettes, are toxic.

According to a study, reported in the ACS journal Environmental Science and Technology, when e-liquid flavourings are heated inside electronic nicotine-delivery systems, the flavourings break down into toxic compounds at levels that exceed occupational safety standards.

The researchers analysed vapours created from both unflavoured and flavoured e-liquids loaded into three popular types of e-cigarettes.

The results showed that in general, one puff of flavoured vapour contained levels of aldehydes exceeding the safe thresholds for occupational exposure -- set by the American Conference of Governmental Industrial Hygienists -- by factors of 1.5 to 270. Vapours from unflavoured e-liquids contained aldehydes at significantly lower levels.

Electronic cigarettes were first introduced to the market in 2003 and health officials have been tracking usage and studying potential health effects.

A 2015 survey by the National Centre for Health Statistics reported that 3.7 per cent of adults used the devices regularly and 12.6 per cent had tried them at least once.