Two potentially harmful compounds were also found in many of the tested flavours. (Representational Image)
A flavouring chemical linked to cases of severe respiratory disease has been found in more than 75 per cent of flavoured electronic cigarettes and refill liquids tested by Harvard researchers.
Two other potentially harmful compounds were also found in many of the tested flavours, which included varieties with potential appeal to young people such as cotton candy, fruit squirts and cupcakes, researchers said.
Researchers at Harvard TH Chan School of Public Health tested 51 types of flavoured e-cigarettes and liquids sold by leading brands for the presence of diacetyl, acetoin, and 2,3-pentanedione, two related flavouring compounds that are listed as 'high priority,' which means they may pose a respiratory hazard in the workplace.
Each e-cigarette was inserted into a sealed chamber attached to a lab-built device that drew air through the e-cigarette for eight seconds at a time with a resting period of 15 or 30 second between each draw. The air stream was then analysed.
At least one of the three chemicals was detected in 47 of the 51 flavours tested. Diacetyl was detected above the laboratory limit of detection in 39 of the flavours tested. Acetoin and 2,3-pentanedione were detected in 46 and 23 of the flavors, respectively.
"Recognition of the hazards associated with inhaling flavouring chemicals started with 'Popcorn Lung' over a decade ago," said Joseph Allen, who led the study.
"However, diacetyl and other related flavouring chemicals are used in many other flavors beyond butter-flavoured popcorn, including fruit flavours, alcohol flavours, and, we learned in our study, candy flavoured e-cigarettes," said Allen.
"Since most of the health concerns about e-cigarettes have focused on nicotine, there is still much we do not know about e-cigarettes," said David Christiani, professor of environmental genetics.
"In addition to containing varying levels of the addictive substance nicotine, they also contain other cancer-causing chemicals, such as formaldehyde, and as our study shows, flavouring chemicals that can cause lung damage," said Christiani.
There are currently more than 7,000 varieties of flavoured e-cigarettes and e-juice (liquid containing nicotine that is used in refillable devices) on the market. The findings were published in the journal Environmental Health Perspectives.