Diacetyl
Diacetyl is FDA GRAS as an oral flavoring at typical food levels and is a natural fermentation product (e.g., in butter, beer). However, inhalation of diacetyl vapors causes severe and irreversible bronchiolitis obliterans ('popcorn lung') in occupational settings.
What it is
2,3-butanedione, a vicinal diketone with a strong butter-like flavor; produced by fermentation or chemical synthesis.
Buttery flavoring agent.
Why it's flagged
- Occupational inhalation hazard (bronchiolitis obliterans) — not relevant to dietary ingestion
What regulators actually say
"NIOSH research found artificial butter flavorings added to popcorn caused disease... NIOSH established recommended exposure limits (RELs) of 5 ppb for diacetyl as 8-hour time-weighted averages."
"Workplace exposure to diacetyl has been associated with severe respiratory impairment and bronchiolitis obliterans."
Regulatory status
United States — FDA
GRAS as flavoring agent for ingestion (21 CFR 184.1278)
European Union — EFSA
Permitted as flavouring substance (FL 07.052)
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