Diacetyl
Butter flavour on microwave popcorn — lung scars in workers.
At a glance
- Also known as
- 2,3-Butandion · Butanedione
- CAS number
- 431-03-8
- Toxicity
Very high
- Carcinogenic
- Not classified for cancer
- In cigarette smoke
- 200-400 μg per cigarette (DKFZ — bei aromatisierten Marken höher)
- In vape aerosol
- wechselnde Mengen in buttrigen/cremigen Aromen; EU-Tabakerzeugnis-Richtlinie verbietet ab 2016 die Verwendung in E-Liquids
What is Diacetyl?
Diacetyl (2,3-butanedione) is a yellowish liquid with an intense butter smell and a natural component of dairy products. Approved in food as a flavouring for decades, it became notorious as an inhalation hazard in the 2000s: workers at a US popcorn factory developed a severe irreversible lung disease — „popcorn lung“ or bronchiolitis obliterans.
Why is Diacetyl in cigarettes?
Diacetyl forms during combustion of added sweeteners and flavourings in tobacco and reaches 200 to 400 micrograms per cigarette in the mainstream smoke (source: DKFZ). In vape flavours it was commonly used before 2016 in „creamy“ or „buttery“ profiles; since then it's banned in the EU for e-liquids under the Tobacco Products Directive — in the USA and many other markets, gaps remain.
What Diacetyl does to your body — short term
Acutely, diacetyl irritates eyes, nose and airways. At the low concentrations encountered through flavouring consumption, symptoms are mild and short-lived. The truly problematic feature is the delayed effect: diacetyl binds to proteins in the smallest bronchi (bronchioles) and there, over weeks to months, triggers an inflammatory and scarring reaction that initially goes unnoticed.
What Diacetyl does long term
The resulting disease is bronchiolitis obliterans, first described in 2002 in workers at a Missouri popcorn factory. It's a progressive scarring of the smallest airways that makes exhalation increasingly difficult. It's not curable — advanced cases require lung transplantation. Among smokers and vape users, bronchiolitis obliterans cases have been increasingly reported, though the prevalence data is still incomplete.
Where else do you know Diacetyl from?
You know diacetyl as what makes microwave popcorn taste like butter — the butter flavour isn't butter, it's diacetyl. It occurs naturally in beer (especially in lagers as an unwanted fermentation product), in butter, cheese and some wines. In all these oral applications it's safe; the risk arises only from inhalation in industrial flavour processing or via vaporisation in e-cigarettes.
How it compares
NIOSH's recommended exposure limit for diacetyl is 0.018 mg/m³ (5 ppb as an 8-hour TWA) and 0.09 mg/m³ (25 ppb as a 15-minute STEL, NIOSH REL 2016) — one of the lowest flavour-substance limits in existence. A cigarette sets the diacetyl concentration in the breathing space to many times these values for a few seconds; with diacetyl-containing e-liquids, exposure over many puffs per day is even more concentrated.
Workplace exposure limit: 0.018 mg/m³ (5 ppb 8h-TWA); STEL 0.09 mg/m³ (25 ppb, 15 min), NIOSH REL 2016
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