Commercial flavorings used in the food service industry are often complex mixtures of flavoring chemicals, many of which are volatile, meaning that they evaporate into the air from their liquid or solid form. Diacetyl is a prominent chemical ingredient in butter flavorings and is a component of the vapors coming from these and other flavorings. Inhalation of butter flavoring chemical mixtures, including diacetyl, has been associated with severe obstructive lung disease popularly know as "popcorn lung." In many symptomatic individuals exposed to flavoring who have undergone lung biopsy, an irreversible type of lung damage called constrictive bronchiolitis has been found. In this condition, the smallest airways carrying air through the lungs, the bronchioles, are scarred and constricted. This can decrease or block air movement through these airways.