Overview
Penicillium is one of the most common mold genera found in indoor environments worldwide. The CDC and EPA identify Penicillium, alongside Cladosporium and Aspergillus, as the molds most frequently detected in indoor air samples.
Best known as the source of the antibiotic penicillin (discovered in Penicillium notatum in 1928), this genus includes over 300 species. While many are harmless or even beneficial, several species can cause allergic reactions and respiratory symptoms when they colonize indoor spaces.
Did You Know: Penicillium colonies often appear blue-green and have a characteristic musty odor. The “blue cheese mold” used in food production (P. roqueforti) belongs to this genus.
Common Indoor Species
Several Penicillium species are commonly found in indoor environments:
Penicillium chrysogenum
The most common indoor Penicillium species. Produces blue-green colonies. Frequently found on damp building materials, wallpaper, and carpet. Allergenic in sensitive individuals.
Penicillium expansum
Common on rotting fruits and vegetables. Produces the mycotoxin patulin. Can colonize indoor environments where produce is stored improperly.
Penicillium citrinum
Found in tropical and subtropical climates. Produces the mycotoxin citrinin. Can occur in HVAC systems and on water-damaged materials.
Where Penicillium Is Found
Penicillium is ubiquitous in the environment. Its lightweight spores spread easily through air currents, and the genus tolerates a wide range of conditions.
Indoor Locations
- Water-damaged drywall, wallpaper, and insulation
- Damp carpet and carpet padding
- HVAC systems and ductwork
- Bathrooms and kitchens with poor ventilation
- Food storage areas
- Basement and crawl spaces
- Areas with condensation (windows, cold pipes)
Growth Characteristics
| Factor | Range |
|---|---|
| Temperature | 5-35°C (41-95°F), optimal 20-25°C |
| Relative Humidity | >60%, can grow at lower levels than some molds |
| Appearance | Blue-green, sometimes white edges, powdery texture |
Penicillium is a fast-growing mold that can spread quickly once moisture conditions allow colonization. Some level of Penicillium presence is normal in most indoor environments due to outdoor spore infiltration.
Health Effects
According to the CDC and EPA, Penicillium exposure can cause health effects that vary by individual sensitivity:
Common Symptoms
- Stuffy or runny nose
- Sore throat
- Coughing or wheezing
- Burning or watering eyes
- Skin rash or irritation
Asthma and Allergies
Penicillium is a known allergen that can trigger asthma attacks in sensitized individuals. Allergic reactions may be immediate or delayed, presenting as hay fever-like symptoms including sneezing, runny nose, and red eyes. Prolonged exposure may increase the risk of developing allergic rhinitis or hypersensitivity pneumonitis.
Mycotoxins
Some Penicillium species produce mycotoxins including:
- Patulin (P. expansum) — primarily a food safety concern
- Citrinin (P. citrinum) — nephrotoxic (kidney-affecting)
- Ochratoxin A (various species) — potentially carcinogenic
Important: The CDC does not recommend mold testing to assess health risks, as health effects vary greatly among individuals. If you experience persistent symptoms, consult a healthcare provider.
Testing & Identification
Penicillium is identified through laboratory analysis using microscopy or culture methods. In lab reports, it is sometimes grouped with Aspergillus as “Pen/Asp” because their spores can appear similar under a microscope without culturing.
Microscopic Identification
Penicillium has a distinctive structure called a “penicillus” (Latin for “painter’s brush”) — branching chains of spores that resemble a brush. This structure helps distinguish it from Aspergillus, which has a spherical spore head.
Research & Citations
- Centers for Disease Control and Prevention. “Mold: Basic Facts.” CDC.gov, 2024. https://www.cdc.gov/mold/
- Environmental Protection Agency. “Mold Resources.” EPA.gov, 2024. https://www.epa.gov/mold/
- EPA. “A Brief Guide to Mold, Moisture and Your Home.” EPA 402-K-02-003.