Three in four e-cigarettes were found to use a flavored liquid that has been linked to severe respiratory disease.
SIA reports citing the France 24 that US researchers stated this.
Electronic cigarettes are battery-powered devices that heat a nicotine-containing liquid, which is inhaled much like a cigarette.
Unlike traditional cigarettes, the devices are not regulated by US authorities, leading to concern among some experts that they may be harmful to health -- and that their candy and fruit flavors may appeal to youths and put them at risk of addiction.
For the study in the journal Environmental Health Perspectives, scientists at Harvard University tested flavors that may appeal to young people such as Cotton Candy, Fruit Squirts and Cupcake.
They found that 75 percent of tested samples contained diacetyl, which when inhaled has been linked to the respiratory disease bronchiolitis obliterans -- sometimes called "popcorn lung" because over 10 years ago it was discovered in workers who inhaled artificial butter flavor in microwave popcorn processing facilities.
Of the 7,000 varieties of flavored e-cigarettes, researchers focused on testing 51 types "sold by leading brands for the presence of diacetyl, acetoin and 2,3-pentanedione, two related flavoring compounds that are listed as 'high priority,'" because they may pose a respiratory hazard in the workplace, the study said.
In a lab testing environment, each e-cigarette was attached to a device that drew air through the e-cigarette for eight seconds at a time, with a resting period of 15 or 30 seconds, to mimic the action of a human smoker.