Allergic alveolitis, also known as hypersensitivity pneumonitis, is an inflammatory lung disease caused by inhaling dust or other allergens. Symptoms include fever, coughing, shortness of breath, and fatigue. If left untreated, allergic alveolitis can lead to lung scarring and permanent damage. Synonyms for allergic alveolitis include extrinsic allergic alveolitis, farmer's lung, bird breeder's lung, and mushroom worker's lung. These terms refer to specific causes of the condition, but all fall under the umbrella of allergic alveolitis. Treatment often involves avoiding exposure to the allergen and taking medications to reduce inflammation and ease symptoms. In severe cases, oxygen therapy or even lung transplant may be necessary.