On December 8, 2015, researchers at Harvard University announced that they had examined a small sample of flavored e-cigarette products and found that some contained diacetyl, a chemical suspected of causing respiratory illness. In the wake of this announcement, some news organizations reported that the Harvard paper established a “link” between e-cigarettes and bronchiolitis obliterans, a disease associated with diacetyl exposure.

But the Harvard study did not discuss any connection between diacetyl in e-cigarettes and respiratory illness. The researchers merely noted the presence of diacetyl in e-cigarettes and that diacetyl has been associated with respiratory disease in the industrial context. The study drew no conclusions about the possible health risks that vaping poses to consumers. Instead, the study’s authors recommended that this new potential source of exposure to diacetyl be further evaluated.

While the recent Harvard paper brought significant media attention to diacetyl in e-cigarettes, it was not the first study to explore the issue. Other researches have compared diacetyl in e-cigarettes to that in tobacco cigarettes. One 2014 study assessed the potential effects on consumers’ health and concluded that median diacetyl exposure levels in e-cigarettes were lower than in tobacco cigarettes, some of which also contain diacetyl, “by 1-2 orders of magnitude.” Researchers noted that diacetyl-related risks of e-cigarettes are “totally avoidable” just “by using alternative compounds.”

As the scientific and regulatory communities continue to examine the health effects of vaping, e-cigarette manufacturers may begin to identify which of their products, if any, contain diacetyl, and consider whether an alternative could achieve the same flavor profile. Although, as the Harvard researchers point out, there are currently no rules for labeling e-cigarettes, the recent focus on the contents of e-liquids may lead more manufacturers to place warnings and ingredient lists on product packaging.