Bronchiolitis obliterans is an inflammatory condition that affects the lung's tiniest airways, the bronchioles. In affected people, the bronchioles may become damaged and inflamed leading to extensive scarring that blocks the airways. Symptoms of the condition include a dry cough; shortness of breath; and/or fatigue and wheezing in the absence of a cold or asthma. Many different chemicals (such as nitrogen oxides, ammonia, welding fumes or food flavoring fumes) and respiratory infections can cause lung injury that leads to Bronchiolitis obliterans. It can also be associated with rheumatoid arthritis and graft-versus-host disease following a lung or hematopoietic cell transplantation. Another similarly named disease, Bronchiolitis obliterans organizing pneumonia, is a different disease.