What is Diacetyl?

Diacetyl (also called butanedione or butane-2,3-dione) is an organic compound with the chemical formula (CH₃CO)₂. It is a yellow/green, volatile liquid with a strong buttery aroma and taste.

Diacetyl naturally forms during beer and wine fermentation as yeast breaks down glucose into ethanol. It’s also found in small amounts in coffee, vinegar, honey, dairy, and fruits.

At low levels, it adds a slippery texture to drinks, while at higher levels, it gives off a butterscotch-like flavour. It has been used as a marker for flavouring vapour exposure, especially in industries like microwave popcorn manufacturing.

Other similar chemicals used as possible substitutes include acetoin, 2,3-pentanedione, 2,3-hexanedione, and 2,3-heptanedione.

What is Diacetyl used for?

Diacetyl is mainly used as a food flavouring. It is commonly added to:

• Flour
• Chocolate
• Cooking oils
• Candy
• Chips
• Frosting
• And most famously, microwave popcorn for its buttery aroma and taste.

Sources and Routes of Exposure

Source of Exposure

Most exposure to diacetyl happens at work in food and flavouring facilities. While it is safe to eat in small amounts, it is not well-tested for safety when inhaled.

Industries where workers may breathe in diacetyl vapours include:

• Flavouring production facilities
• Microwave popcorn factories
• Commercial and retail bakeries
• Snack food and candy factories
• Dairy and vegetable oil plants (e.g., margarine and cooking oil)
• Other flavoured food processing plants

Routes of Exposure

Diacetyl enters the body mainly by:

• Inhalation
• Ingestion

Health Effects

Acute Effects

Short-term exposure to diacetyl can cause:

• Eye irritation or chemical burns from vapours
• Skin irritation, rash, redness, dryness, and cracking
• Throat and nose irritation, coughing, and wheezing
• At high levels: headache, drowsiness, poor coordination, and seizures

Chronic Effects

Long-term or repeated exposure can lead to serious lung damage, especially in workers. This includes a rare condition called bronchiolitis obliterans (also known as “popcorn lung”), which causes:

• Dry cough
• Shortness of breath (especially with exertion)
• Wheezing
• Permanent lung damage

Asthma medications do not help, and some affected workers may not show symptoms at all. Diacetyl has also caused lung damage in test animals.

Reproductive Hazard

Diacetyl has not been tested for its effect on reproduction.

Cancer Risk

Diacetyl has not been tested for its ability to cause cancer.

Medical Testing

Testing for diacetyl exposure may include:

• Spirometry: Shows impaired airflow that does not improve with bronchodilators
• Lung volumes: May show hyperinflation
• CO diffusing capacity: Often normal in early disease
• Chest X-rays: Usually normal but can show hyperinflation
• CT scans: May show air trapping, mosaic patterns, bronchial wall thickening, or ground-glass opacities
• Lung biopsies: Not usually required, but may confirm bronchiolitis obliterans

Safety

First Aid Measures

• Inhalation: Move to fresh air. Give artificial respiration or oxygen if needed.
• Skin Contact: Wash immediately with soap and water.
• Eye Contact: Rinse eyes for at least 15 minutes with water.
• Ingestion: Rinse mouth with water. Do not induce vomiting. Call a doctor.

Fire & Explosion Information

• Flammable liquid
• Releases toxic fumes during fires
• Vapours may travel and ignite at a distant source
• Containers can explode when heated
• Forms explosive air mixtures

Exposure Control & Personal Protection

Engineering Controls

• Use a safety shower and eyewash station
• Use non-sparking tools
• Provide mechanical exhaust ventilation

General Hygiene Measures

• Remove and wash contaminated clothing immediately
• Wash hands and exposed skin thoroughly after handling

Personal Protective Equipment (PPE)

• Respiratory Protection: Use approved respirators (e.g., NIOSH or EN 14387 type ABEK)
  • Use full-face respirators if needed
• Hand Protection: Wear chemical-resistant gloves
• Eye Protection: Use chemical safety goggles

Regulation

United States

Australia

No regulation established