New York, Dec 8 (IANS): A flavouring chemical linked to a severe respiratory disease has been found in more than 75 percent of flavoured electronic cigarettes and refill liquids tested by researchers at Harvard University.

Two other potentially harmful related 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 Cupcake, said the team from Harvard's T.H. Chan School of Public Health.

Recognition of the hazards associated with inhaling flavouring chemicals started with “Popcorn Lung” over a decade ago.

“However, diacetyl and other related flavouring chemicals are used in many other flavours beyond butter-flavoured popcorn, including fruit flavours, alcohol flavours and candy flavoured e-cigarettes," explained lead study author Joseph Allen, assistant professor of exposure assessment science.

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.

Allen and colleagues 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”.

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 and of the flavours, respectively.

Most of the health concerns about e-cigarettes have focused on nicotine, but there is still much we do not know about e-cigarettes.

“In addition to containing varying levels of the addictive substance nicotine, our study shows that flavouring chemicals can also cause lung damage,” said study co-author David Christiani.

The study is forthcoming in the journal Environmental Health Perspectives.