What Is Cladosporium?

Cladosporium is the most frequently detected mold genus in indoor air samples worldwide. It is an extremely successful environmental organism, producing enormous quantities of small spores (2–7 microns) that travel easily in air currents. Unlike Stachybotrys, Cladosporium can grow at lower moisture levels, meaning it can colonize surfaces that are merely damp rather than continuously saturated.

You are most likely to find Cladosporium on window frames and sills (where condensation collects), bathroom grout, wooden furniture and window trim, HVAC duct surfaces, and on fabrics or carpets in damp rooms. It typically appears as a dark olive-green to black powdery growth, sometimes with a suede-like texture.

Cladosporium is classified as a major allergen and is one of the most common causes of mold-triggered allergic rhinitis and asthma worldwide. While it does not produce the severe mycotoxins associated with Stachybotrys, some species produce trace amounts of secondary metabolites that can irritate airways. The primary health concern is immune sensitization — once a person becomes allergic to Cladosporium spores, even normal outdoor spore levels can trigger symptoms.

Control measures focus on reducing indoor humidity. Keeping relative humidity below 50–55% deprives Cladosporium of the moisture it needs to grow. Regular cleaning of window frames, ensuring HVAC system components stay dry, and using exhaust fans in bathrooms and kitchens are practical prevention steps. Visible Cladosporium colonies on hard non-porous surfaces can typically be cleaned with appropriate antifungal cleaners, but porous materials like drywall or wood with deep penetration require professional remediation.