A common saprobe found on decaying wood, decaying plants, food, spoil and outdoor air. Some species are plant pathogens. Indoors, it can be found in house dust, carpets, damp areas around showers and windows frames and anywhere condensation occurs. Because of its abundance and ubiquity, Alternaria is one of the most important fungal allergens and is recognized as the chief fungal cause of hay fever. Infection is extremely rare.