evidence: Aspergillosis is an infection caused by a type of mold (fungus). The illnesses resulting from aspergillosis infection usually affect the respiratory system, but their signs and severity vary greatly. The mold that triggers the illnesses, aspergillus, is everywhere — indoors and outdoors. Most strains of this mold are harmless, but a few can cause serious illnesses when people with weakened immune systems, underlying lung disease or asthma inhale their fungal spores. [...] It's nearly impossible to avoid exposure to aspergillus, but if you have had a transplant or are undergoing chemotherapy, try to stay away from places where you're likely to encounter mold, such as construction sites, compost piles and buildings that store grain. If you have a weakened immune system, your doctor may advise you to wear a face mask to avoid being exposed to aspergillus and other airborne infectious agents.