Aspergillus is a common type of fungus that grows on decaying vegetation, such as compost heaps and fallen leaves. It can also be found in air-conditioning systems and hospitals. Some people with asthma are allergic to the fungal spores. These can trigger an asthma attack if inhaled. Some people will develop a condition known as allergic bronchopulmonary aspergillosis (ABPA), in which asthma worsens significantly as a result of increased lung inflammation. Several species of Aspergillus, including A. fumigatus, A. niger, A. flavus, and A. oryzae, are allergic.