Aspergillosis is a fungal infection caused by Aspergillus, a species of mold that is found all over the world. More than 180 different types of Aspergillus have been identified and more are continuing to be identified. Most of these molds are harmless. However, some types can cause a variety of diseases in humans ranging from simple allergic reactions to life-threatening invasive disease. Collectively, this group of diseases is referred to as aspergillosis and is broadly broken down into three categories - allergic, chronic and invasive. There are several different forms including allergic bronchopulmonary aspergillosis, allergic Aspergillus sinusitis, invasive aspergillosis, cutaneous (skin) aspergillosis, and chronic pulmonary aspergillosis, which also has several different presentations. Aspergillosis rarely develops in healthy individuals; most people breathe in these spores every day without any issues. An infection is much more likely to develop in individuals who have an underlying condition such as asthma, cystic fibrosis, and previous lung disease, or who have taken corticosteroid drugs for a long period of time, or in individuals who have a weakened immune system, including people who have low levels of neutrophils, a type of white blood cell that helps the body fight off infection and heal itself (neutropenia), or who are taking drugs that suppress the immune system (immunosuppressive drugs) such as people who have had a bone marrow or organ transplant. In most instances, aspergillosis develops when susceptible individuals breathe in (inhale) Aspergillus spores. Aspergillosis is not contagious and cannot be transmitted from one person to another.