Posted February 23, 2012 by Jack Keenan in About e-Cigarettes

What are Diacetyl, Acetyl Propionyl and Acetoin?

Diacetyl Electronic Cigarettes E-Liquid
Diacetyl Electronic Cigarettes E-Liquid

Disclaimer: I am not a doctor, nor do I claim to be an expert on food or chemical safety. This article is a summary of my personal research, conducted on websites intended for laypeople. It is presented for informational purposes only and I take no responsibility for any damage caused by the use or misuse of the information contained within. If you have health concerns about diacetyl, acetyl propionyl or electronic cigarettes in general, ask your doctor.

I was recently browsing the Halo Cigs E-Liquid FAQ and found some information about a term with which I was not familiar: diacetyl. Here are the question and answer, taken from the FAQ:

Does your e-liquid contain Diacetyl?


No, Halo does not contain Diacetyl in any of our e-liquid formulas. This was a strict requirement for Halo far before it became a popular topic in the forums. In addition, our e-liquid also does not contain Acetyl, Propionyl, 2-3 Hexanedione, 2-3 Heptanedione, or Diacetyl Trimer which are often used as Diacetyl equivalents. 

It seems that it is — or was — common for e-liquid manufacturers to use diacetyl in constructing their flavors, and the phrasing of this entry in the Halo FAQ led me to believe that it might be a dangerous substance, so I did a bit of research. I thought that I would post my findings here for any readers who might be curious about diacetyl, how it relates to e-liquids and whether it might pose any health concerns.

What is Diacetyl?

According to Wikipedia, diacetyl is a substance that occurs naturally during fermentation. It is one of the key flavor components of butter, and as a result, food companies may use it as a flavoring agent for products such as margarine and microwave popcorn. Diacetyl gives those products a buttery taste and smell while reducing the fat, calories and cholesterol associated with using pure butter. In 1980, the United States Food and Drug Administration gave diacetyl the label “Generally Recognized as Safe,” or “GRAS.” When a substance is placed on the GRAS list, it essentially means that it has enough support from experts that the FDA has decided to exempt it from testing and declare it safe for its intended purpose. Diacetyl, for example, has been declared safe for use as a food flavoring agent.

However, controversy began to arise in the early 2000s when workers at popcorn factories contracted a devastating disease called bronchiolitis obliterans. The disease has since come to be known as “popcorn worker’s lung.” Apparently, when heated and inhaled in massive quantities, diacetyl can cause severe and permanent damage to the lungs. The only known treatment for extreme cases is a lung transplant. The United States Occupational Safety and Health Administration (OSHA) has since issued an advisory essentially recommending that workers regularly in contact with diacetyl wear equipment to protect their skin and lungs. Although pressure has been placed on the FDA to reevaluate the GRAS status of diacetyl, it remains in use as a food additive. However, some popcorn companies have apparently stopped using it. According to Wikipedia, the Trail’s End, Orville Redenbacher’s and Act II microwave popcorn brands no longer contain diacetyl.

Diacetyl and Electronic Cigarette E-Liquids

So, what does all of this mean to you as an electronic cigarette user? Electronic cigarettes turn e-liquid to vapor by heating it, and whatever the e-liquid contains is concentrated in the lungs when you inhale it. Although diacetyl remains a common food additive, the available evidence suggests that it is not a safe substance to inhale. If your favorite e-liquid has the taste or smell of butter, I would suggest asking the manufacturer whether it contains diacetyl. I have noticed that many American e-liquid companies have been quick to post notices on their websites stating that none of their e-liquids contain diacetyl; if you don’t see this notice on your favorite manufacturer’s website, it would benefit you as well as the manufacturer if you asked them to conduct some research and find out what substances their e-liquids contain.

What About Acetyl Propionyl and Acetoin?

Many companies have moved away from diacetyl as a means of imparting a buttery scent and taste to their foods. As a result, those companies have needed to find alternatives for customers who want butter-flavored products but are watching their intake of calories, fat and cholesterol. My research suggests that acetyl propionyl and acetoin are two of the most common substances these companies are using, and as a result, any e-liquid that has a buttery flavor but does not contain diacetyl may contain one of these chemicals. Acetyl propionyl may also be known as 2,3-pentanedione. Apparently, this substance is structurally similar to diacetyl and is considered a respiratory irritant. According to the Perfumer’s Apprentice, trace amounts of diacetyl may be created during the production of acetoin. This makes sense since diacetyl and acetoin are both naturally found in butter. As a result, flavoring agents using acetoin to achieve a buttery scent and flavor may contain trace amounts of diacetyl even if diacetyl was not specifically added to the flavor. Interestingly, according to Wikipeda, acetoin may also be found as an additive in cigarettes. Although it is not currently known whether it is dangerous to inhale e-liquids containing acetoin or acetyl propionyl, it may also be wise to ask e-liquid manufacturers if they use either of these chemicals.