Hypersensitivity pneumonitis (HP) is a cell-mediated immune reaction to inhaled antigens in susceptible persons [94, 95] . In children, HP is often associated with exposure to antigens in the home environment as well as with certain hobbies. The most frequent types of HP include bird fancier's diseases, humidifier lung diseases, and chemical lung diseases. Bird fancier's diseases are induced by exposure to birds with the antigens being glycoproteins in avian droppings, and on feathers. Importantly, respiratory symptoms in exposed patients who have only one pet bird at home should raise the suspicion of HP [96] . Humidifier lung diseases (air conditioner lung, misting fountain lung, basement lung diseases) are caused mainly by free-living amoeba and nematodes, as well as bacteria and fungi. Chemical lung diseases can be induced by various inorganic antigens such as those from vaporized paints and plastics. Low-molecular-weight chemicals may react with proteins in the airways, thus forming complete antigens. Once exposure history is obtained, additional information is required and includes biologic tests allowing measurements of environmental contaminants and interpretation of the results by environmental medicine experts.