Aspergillus is a genus of fungi with over 150 species. Many species produce mycotoxins associated with disease in humans. Found in a variety of environments most frequently thriving as saprophytes on decayed material. Some species are parasitic to man, animals, plants and insects. Aspergillus and several related fungi are the considered cause of aspergillosis and similar Aspergillus species are highly aerobic and are found in almost all oxygen-rich environments, where they commonly grow as molds. It can be found growing on damp walls, as a major component of mildew. Some Aspergillus species cause serious disease in humans and animals, and can be pathogenic. Aspergillosis is the group of diseases caused by Aspergillus. The symptoms include fever, cough, chest pain or breathlessness, which also occur in many other illnesses so diagnosis can be difficult. Usually, only patients with already weakened immune systems or who suffer other lung conditions are susceptible.