Cladosporium
Cladosporium is a common mold type frequently found both in and outdoors, especially in humid or poorly ventilated areas. It can grow on a wide variety of household surfaces—from walls and carpets to HVAC vents and window sills—and is known for its dark, soot-like appearance. While most mold species aren’t highly toxic in small amounts, Cladosporium can trigger allergic reactions, respiratory irritation, and asthma flare-ups in sensitive individuals or pets, particularly when exposure is prolonged or indoor humidity remains high.
Cladosporium is one of the most common types of household and outdoor molds. It’s a genus with hundreds of species that thrive almost everywhere—from decaying plants and soil to damp indoor surfaces. While it’s not the most dangerous mold out there, it’s certainly one of the most widespread and persistent. Its spores are easily airborne, meaning it can spread quickly through both indoor and outdoor air.
Under the microscope, Cladosporium spores are small—typically around 3–6 micrometers in diameter. To the naked eye, its growth tends to appear as olive-green, brown, or black patches with a velvety or powdery texture. On surfaces like walls or fabrics, it can look like soot or dark smudges, which sometimes makes it easy to mistake for dirt.
Outdoors, Cladosporium thrives on decaying leaves, plant matter, and wood. Indoors, it often shows up on bathroom walls, window sills, HVAC vents, carpets, and behind wallpaper—basically anywhere that’s slightly damp and poorly ventilated. It’s also one of the most common molds found in air conditioning systems and around condensation-prone areas.
While Cladosporium doesn’t need standing water to grow, it does require consistent humidity or dampness. It can even survive in relatively cool environments, which is why you might find it on cold surfaces like metal or glass where condensation forms. Keeping indoor humidity below 50% is key to preventing its growth.
For most healthy people, Cladosporium is more of an allergen than a toxin. It’s a common trigger for hay fever–like symptoms such as sneezing, runny nose, itchy eyes, and coughing. In sensitive individuals—especially those with asthma, allergies, or weakened immune systems—it can cause respiratory irritation or worsen existing conditions. Pets can also experience allergic reactions, often showing signs like sneezing, coughing, or skin irritation.
While it’s not typically associated with severe infections, chronic exposure in poorly ventilated spaces can lead to persistent health discomfort.
The best prevention strategy for all mold types is moisture control. Fix leaks promptly, use dehumidifiers in humid areas, and ensure good airflow—especially in bathrooms, kitchens, and basements. Regularly clean HVAC filters and vents, and keep condensation-prone surfaces dry.
If any mold species covers an area larger than about 10 square feet, keeps returning after cleaning, or is growing inside HVAC ducts or porous materials (like drywall or insulation), it’s time to call a professional. Cladosporium growth can indicate a deeper moisture problem that needs expert evaluation. If anyone in the home experiences worsening respiratory symptoms, professional mold assessment is strongly recommended.
