There are more than 7,000 types of flavored e-cigarettes and liquids on the market today.
In 47 of the 51 types of flavored electronic cigarettes (e-cigarettes) and e-juice tested by the researchers, at least one of three potentially harmful chemicals were present.
The new study, published in Environmental Health Perspectives, addresses a gap in e-cigarette research; although there are over 7,000 kinds of flavored e-cigarettes and e-juice available for purchase, few studies have examined exposure to flavoring chemicals.
Flavoring chemicals came under scrutiny in the early 2000s, after reports surfaced of severe bronchiolitis obliterans - a harmful respiratory condition that can, in severe cases, only be treated by lung transplant - among workers at a microwave-popcorn processing plant.
This condition has since come to be referred to as "popcorn lung," and its development was associated with the inhalation of butter flavoring chemical mixtures. The most prominent of these was diacetyl.
"However, diacetyl and other related flavoring chemicals are used in many other flavors beyond butter-flavored popcorn, including fruit flavors, alcohol flavors, and, we learned in our study, candy-flavored e-cigarettes," explains lead author Joseph Allen, assistant professor of exposure assessment science.
The flavorings used in the popcorn were listed on the Generally Recognized As Safe (GRAS) list, however, this declaration of safety applied only to ingestion rather than exposure to the chemicals via inhalation, a process about which very little was known.
Diacetyl and two other flavoring compounds - acetoin and 2,3-pentanedione - are found in a number of other flavorings in addition to butter, including many that can be found in e-cigarette flavoring cartridges.
Potentially harmful chemicals found in 92% of flavors tested
Prof. Allen and his team hypothesized that these compounds were likely to be found in flavored e-cigarettes, and so they set out to test 51 types of flavored e-cigarettes and liquids sold by leading brands for each of the three chemicals.
Testing was conducted by placing the e-cigarette inside a sealed chamber where a device would draw air through it for 8 seconds at a time, followed by a rest period of 15-30 seconds. The researchers then analyzed the airstream in the chamber for the three chemicals.
Diacetyl was found in 47 of the 51 flavors tested. Acetoin was detected in 46 of the flavors, and 2,3-pentanedione was found in 23 of the flavors. In total, 92% of the flavors tested contained at least one of the three chemicals.
Surprisingly, the researchers found that "tobacco" and "menthol" flavored e-cigarettes contained diacetyl, despite the fact that these flavors are not on the Occupational Safety and Health Administration's (OSHA) list of flavors that likely contain the chemical.
The researchers conclude that due to the associations between diacetyl and severe respiratory diseases, urgent action is recommended to further evaluate exposure to the chemicals via e-cigarette use.
"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, flavoring chemicals that can cause lung damage," concludes study co-author Prof. David Christiani.
Are flavorings more attractive to children and teens?
Of additional concern to the authors is how some of these flavorings may be particularly appealing to children and teenagers, with some advertised with names such as Cupcake, Cotton Candy, Fruit Squirts and Alien Blood.
Medical News Today previously reported on a study that suggested flavored tobacco products may be responsible for attracting some young people to start smoking. The Centers for Disease Control and Prevention (CDC) estimate that 1.78 million children had used e-cigarettes as of 2012, with 160,000 of these children reporting having never used tobacco cigarettes.
Recent years have seen e-cigarettes reach greater heights of popularity than ever before. According to the World Health Organization (WHO), $3 billion was spent on e-cigarettes in the US, and sales are expected to have risen 17 times over the next 15 years.
Despite their popularity, e-cigarettes are not regulated in the US at present, although the US Food and Drug Administration (FDA) have proposed to include e-cigarettes within their regulation of other products containing tobacco and nicotine.
Until this proposal is passed, there remains a need for researchers to investigate e-cigarettes, to ensure that this valuable tool for smoking cessation can be made as safe as possible.
Earlier this year, MNT reported on an independent review of scientific literature concluding that using e-cigarettes is 95% less harmful than smoking combustible tobacco products.