Aspergillosis is a fungal infection of usually the lungs, caused by the genus Aspergillus, a common mold that is breathed in frequently from the air around, but does not usually affect most people. It generally occurs in people with lung diseases such as asthma, cystic fibrosis or tuberculosis, or those who have had a stem cell or organ transplant, and those who cannot fight infection because of medications they take such as steroids and some cancer treatments. Rarely, it can affect skin.