Overview
Cladosporium is the most commonly identified mold genus in both indoor and outdoor air samples worldwide. Research consistently ranks it as either the most abundant or second-most abundant mold in indoor environments, often alongside Aspergillus and Penicillium.
This genus includes over 700 species, with several commonly found in residential and commercial buildings. Unlike some molds that require very wet conditions, Cladosporium can grow at relatively low moisture levels, making it a frequent colonizer of slightly damp building materials.
While Cladosporium rarely causes severe health effects in healthy individuals, it ranks among the most important fungal allergens. Sensitization to Cladosporium is common in atopic individuals and has been associated with allergic rhinitis and asthma exacerbation.
Key Point: Because Cladosporium is so prevalent outdoors, finding some spores in indoor air samples is normal and expected. Interpretation requires comparing indoor levels to outdoor baseline samples.
Common Cladosporium Species
Three species account for the majority of Cladosporium found in indoor environments:
Cladosporium herbarum
The most common species in outdoor air. Primarily found on decaying plant material, leaves, and soil. Enters buildings through open windows, doors, and HVAC systems. Peak counts occur during warm, humid months.
Cladosporium cladosporioides
Frequently found both indoors and outdoors. Common on damp building materials, painted surfaces, textiles, and food products. Can grow at temperatures as low as 0°C (32°F), making it capable of colonizing refrigerated environments.
Cladosporium sphaerospermum
Commonly found in bathrooms, kitchens, and other humid indoor locations. Frequently colonizes painted surfaces, wallpaper, and window frames where condensation occurs. Often indicates chronic moisture issues.
Where Cladosporium Is Found
Indoor Locations
- Window sills and frames (condensation accumulation)
- Bathroom surfaces, especially around showers and tubs
- HVAC systems, ductwork, and air conditioning coils
- Painted surfaces and wallpaper in humid areas
- Carpets and textiles in damp environments
- Refrigerator gaskets and interiors
- Damp basement and crawl space surfaces
- Behind furniture placed against exterior walls
Outdoor Sources
- Dead and decaying plant material
- Leaf litter and compost
- Soil surfaces
- Rotting wood and wooden structures
- Agricultural crops (wheat, corn, tomatoes)
- Tree bark and forest environments
Growth Conditions
Cladosporium is notable for its ability to grow under a wider range of conditions than many other molds:
| Factor | Range | Notes |
|---|---|---|
| Temperature | 0-35°C (32-95°F) | Can grow at refrigerator temperatures |
| Water Activity (aw) | 0.84-0.88 minimum | Lower than many molds; can grow in drier conditions |
| Relative Humidity | >60% sustained | Will colonize surfaces in moderately damp environments |
| Appearance | Olive-green to brown-black | Velvety or powdery texture |
Early Warning Indicator: Because Cladosporium can grow at lower moisture levels than many molds, its presence on indoor surfaces may indicate a developing moisture problem before other molds appear.
Health Effects
Allergic Reactions (Primary Concern)
Cladosporium is one of the most significant fungal allergens worldwide. Research from the American Academy of Allergy, Asthma & Immunology identifies it as a major trigger for:
- Allergic rhinitis — Sneezing, runny nose, nasal congestion
- Allergic conjunctivitis — Itchy, watery, red eyes
- Asthma exacerbation — Wheezing, chest tightness, shortness of breath
- Hypersensitivity pneumonitis — Rare; occurs with heavy, prolonged exposure
Skin and Nail Infections (Uncommon)
Cladosporium can occasionally cause superficial infections such as onychomycosis (nail fungal infection) and skin lesions. Deep or invasive infections are extremely rare, occurring almost exclusively in severely immunocompromised individuals.
Mycotoxins
Unlike some molds (e.g., Stachybotrys, Aspergillus), Cladosporium is not typically associated with significant mycotoxin production. While some species can produce minor metabolites, these are not considered a primary health concern from typical indoor exposure.
Medical Note: If you experience persistent allergy symptoms that worsen indoors, consult an allergist or immunologist. Skin prick testing or blood tests can identify specific mold sensitivities.
Testing & Identification
Visual Identification
Cladosporium colonies typically appear olive-green to brown-black with a velvety or powdery surface texture. However, visual identification alone is unreliable — laboratory analysis is required for definitive identification.
Microscopic Features
Under microscopy, Cladosporium spores are distinctive: ellipsoidal to lemon-shaped, often in branching chains. Spores have dark pigmentation and visible scars where they were attached to the chain. These features make them readily identifiable by trained analysts.
Interpreting Test Results
Because Cladosporium is the most common outdoor mold, indoor samples typically contain some spores from outdoor infiltration. Key interpretation principles:
- Compare indoor counts to outdoor baseline samples collected simultaneously
- Indoor counts significantly exceeding outdoor levels suggest indoor amplification
- Presence on surface samples indicates active colonization, not just infiltration
- Species identification may provide additional insight (e.g., C. sphaerospermum is more common indoors)
Cladosporium in Oklahoma
Oklahoma’s climate creates favorable conditions for Cladosporium prevalence:
Seasonal Patterns
Outdoor Cladosporium counts in the OKC metro typically peak from late spring through fall (May-October), with highest concentrations during warm, humid periods. Counts drop significantly during winter months but never reach zero.
Humid Summers
Oklahoma’s humid summer months (often 70-80% relative humidity) can drive indoor humidity levels above the 60% threshold where Cladosporium thrives, especially in homes without adequate air conditioning or dehumidification.
Common Problem Areas
In Oklahoma homes, TrueSight commonly finds Cladosporium on bathroom surfaces, window condensation areas, HVAC components, and crawl spaces — particularly in older homes with less efficient climate control systems.
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/
- American Academy of Allergy, Asthma & Immunology. “Mold Allergy.” AAAAI.org.
- Asthma and Allergy Foundation of America. “Mold Allergies.” AAFA.org, 2024.
- Bensch K, et al. “Species and ecological diversity within the Cladosporium cladosporioides complex.” Studies in Mycology 2010.
- WHO. “Guidelines for Indoor Air Quality: Dampness and Mould.” World Health Organization, 2009.