With e-cigarettes booming in popularity and being marketed as a healthier alternative to traditional smoking, scientists have been investigating the chemicals used in vaping in an attempt to identify any associated health risks.

Now a new study suggests that e-cigarettes may pose significant harm to vapers, having found that more than 75 percent of the e-cigarette varieties tested contained diacetyl – a flavouring chemical that's previously been linked to the severe respiratory disease, bronchiolitis obliterans.

The debilitating lung condition became commonly known as 'popcorn lung' – or 'popcorn worker's lung' – back in the early 2000s, when it first appeared in food industry workers who inhaled artificial butter flavouring in microwave popcorn processing facilities.

When airborne diacetyl is inhaled from the flavouring over a long period of time, the chemical can reduce air flow in the lungs by obstructing passageways called bronchioles. The chemical is most dangerous to those who are exposed to it persistently in the workplace, although there has been at least one case involving a heavy consumer of microwave popcorn who consumed multiple bags of the food daily for over a decade.

"Recognition of the hazards associated with inhaling flavouring chemicals started with 'popcorn lung' over a decade ago," said Joseph Allen, an exposure assessment expert at the Harvard University T.H. Chan School of Public Health. "However, diacetyl and other related flavouring chemicals are used in many other flavours beyond butter-flavoured popcorn, including fruit flavours, alcohol flavours, and, we learned in our study, candy flavoured e-cigarettes."

With more than 7,000 varieties of flavoured e-cigarettes and e-juice (used in refillable vaping devices) on the market, it would be close to impossible to test them all. For this study, Allen and his team selected 51 types of flavoured e-cigarettes sold by nine different brands, picking flavours based on their potential appeal to children, teenagers, and young adults. Each product was inserted into a sealed chamber attached to a lab-built device that drew air through the e-cigarettes for 8 seconds at a time.

Analysis of the air stream revealed that diacetyl was present in 39 of the 51 flavours tested. When testing for the presence of acetoin and 2,3-pentanedione – two other flavouring compounds that potentially pose a respiratory hazard in the workplace – at least one of the three chemicals was detected in 47 of the 51 flavours tested.

The team includes a full list of the flavours found to contain diacetyl and/or the other chemicals in their paper, published in Environmental Health Perspectives, including Cherry Crush, Peach Schnapps, Vanilla Bean, and Grape Hookah.

The findings tell us more about the potential dangers of e-cigarettes, but they also highlight how we're really only beginning to understand the health implications of this comparatively new drug choice. While the sample size in this study is comparatively small – just 51 flavours out of more than 7,000 on the market, and only representing products from nine brands  – It's definitely something to think about if you choose to vape because you believe that you're not harming your body.

"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 one of the researchers, David Christiani. "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."