Aspergillus and Penicillium are two of the most common mold genera that we see in air samples. When dealing with spore trap lab results, you will often see these types listed together in groups such as Aspergillus/Penicillium, Asp/Pen, or Pen/Asp. Visually, spores of these genera are so similar that analysts can not differentiate them, so they are reported together. Occasionally spores from other genera which produce similar small amerospores (spores with no septations and no projections longer than the length of the spore) will be counted in this group also. Because there are over 200 separate species of both Aspergillus and Penicillium, an Asp/Pen designation on a lab report represents a large grouping of different species.
Since there are so many different species in this group, we can find Aspergillus and Penicillium in a broad range of habitats. Some species such as Aspergillus penicillioides are xerophilic, which means they grow with only a small amount of moisture. Other species like Aspergillus versicolor are more prevalent in environments with high water activity. In a home without any moisture problems you can often find Aspergillus and Penicillium growing on spoiled fruit.
Like all mold, Aspergillus/Penicillium can cause allergic reactions in people who are sensitive to these types. They can also occasionally cause fungal infections of the ear, eyes, and skin. In people with underlying health issues and compromised immune systems, Aspergillus can infect the lungs causing pulmonary aspergillosis.
Surprisingly, mold isn’t always the bad guy. There are many important uses for fungi in industry. For example, Aspergillus and Penicillium are used to make all sorts of products from cheese to pharmaceuticals. Without these fungi we would be without many important antibiotics, soy sauce, or soft drinks.