Workers at various popcorn manufacturing facilities have been diagnosed with a degenerative lung injury that, left untreated, can lead to death. What is the cause of this injury? A chemical called diacetyl-it is the primary ingredient in butter flavoring. Young workers who have been repeatedly exposed to this chemical experience serious lung injury that may require a lung transplant. If you have worked in a plant that makes buttered popcorn, you should have a medical exam to determine how your lungs are doing.