Hypersensitivity pneumonia from the past to the future

HP is an inflammatory and/or fibrotic disease affecting the lung parenchyma and small airways. Exploring the historical context of HP helps to understand how significant changes in risk factors over time have influenced its development. More than 300 etiologic agents have been identified as the cause of the disease. Bacteria, fungi, animal proteins, plant proteins, low molecular weight chemicals, and metals have been identified as inciting agents. Many inciting agents have been associated with HP since its recognition in 1700. New exposures continue to be suspected as causative factors in the development of HP. As occupational and unsalaried avocational practices evolve, give rise to an ever-expanding list of HP-inducing risk factors, including three-dimensional printers (thought to be due to nylon powder used in its manufacture), contaminated home continuous positive airway pressure machines and dental products (methyl acrylates affecting dental technicians).