Abstract Hypersensitivity pneumonitis is a lung disorder showing inflammation and hypersensitivity reactions specifically, the Type-III and Type-IV ones. The disorder is also termed extrinsic allergic alveolitis. The exact cure of this is still unknown. Only way suggested by the physicians is to avoid the pathogen to re-enter or re-encounter. At chronic stages the steroidal therapy is recommended such as corticosteroid (Prednisolone) with or without some anti-allergic agents depending upon the extent and nature of exposure by a patient to a causative pathogen. Since there are several causative factors and organic dusts, the diagnosis sometimes becomes difficult and the exact cause becomes unknown in various cases. The paper focuses on the exact matter which is lesser known or misinterpreted to be some other respiratory disorder or hypersensitivity disorder. This can be classified into 3 stages. Among these, Acute hypersensitivity pneumonitis is the most widespread whereas the chronic hypersensitivity pneumonitis is developed in nearly 5% of the acute ones.