Up to 75 percent of flavored e-cigarette liquids may contain the chemical Diacetyl, which Harvard researchers have linked to respiratory disease.

The Harvard T.H. Chan School of Public Health researchers selected 51 flavors from major brands and found the flavoring compound Diacetyl in 39 of them.

Diacetyl is used in many rich artificial flavors, like popcorn butter, butterscotch, caramel and pina colada.

The Centers for Disease Control list Diacetyl as a workplace hazard if inhaled. Workers in microwave popcorn factories are exposed to the compound when the flavoring is being applied to popcorn because it aerates.

Long-term exposure to Diacetyl can cause a chronic obstructive pulmonary disease that scars lung tissue called Bronchiolitis obliterans. The disease is commonly referred to as “popcorn lung.”

The Harvard study contained a table of flavors known to contain Diacetyl:

e-cigarette flavors known to contain Diacetyl. Harvard.edu

While most research has been geared towards linking vapor-based tobacco as being as harmful as smoke-based tobacco, it seems the well-known flavoring compound slipped under the radar.

A recent FDA opinion released by the Generally Recognized as Safe Substances Committee said Diacetyl was generally safe:

There is no evidence in the available information on diacetyl or starter distillate that demonstrates or suggests reasonable grounds to suspect a hazard to the public when they are used at levels that are now current or that might reasonably be expected in the future.”

But the opinion was based on Diacetyl introduced through food, not through inhalation.

The research team is requesting further research be conducted into Diacetyl flavoring and e-cigarettes.