What Is Aspergillus?

Aspergillus is one of the most common genera of mold on Earth, comprising over 300 identified species. You encounter Aspergillus constantly — it lives in soil, on decaying plant matter, in compost piles, and in household dust. Its spores are so prevalent that most healthy adults inhale hundreds to thousands of Aspergillus spores daily without any ill effect.

The color varies widely by species: Aspergillus niger is typically black, A. flavus is yellow-green, and A. fumigatus is blue-green with a powdery texture. This color variation means that seeing black or green mold does not tell you which species you're dealing with — lab analysis is required for species-level identification.

Health risks from Aspergillus depend heavily on the species and the immune status of the person exposed. Immunocompromised individuals — those on chemotherapy, organ transplant recipients, or people with HIV — can develop invasive aspergillosis, a potentially fatal lung infection. For healthy individuals, Aspergillus mainly causes allergic reactions and, in some cases, allergic bronchopulmonary aspergillosis (ABPA), a chronic lung condition.

Some Aspergillus species (notably A. flavus and A. parasiticus) produce aflatoxins under the right conditions. However, indoor building-associated Aspergillus growth rarely produces significant aflatoxin levels. The more common indoor concern is allergen sensitization and the production of other mycotoxins like ochratoxin A, which some A. niger strains produce.

When Aspergillus is found indoors at elevated levels — particularly in combination with water damage — professional remediation following IICRC S520 protocols is the appropriate response. DIY cleaning without containment and HEPA filtration risks spreading spores throughout the home.