Common Mold Species We Identify

Appearance: Olive-green to brown or black colonies. Under the microscope, lemon-shaped (ellipsoidal) spores form branching, tree-like chains.

Where it's found: Living and dead plant material, soil, and indoors on damp window sills, fabrics, HVAC surfaces and bathrooms.

Why it matters: A very common airborne allergen that can trigger hay-fever-type symptoms and asthma. It rarely infects healthy people. Indoor counts well above outdoor often point to a moisture source.

Appearance: Tiny round spores (3–5 µm) produced in chains. Colonies range from blue-green to yellow to black depending on the species.

Where it's found: House dust, water-damaged building materials, soil and stored food. They grow on many materials with only modest moisture.

Why it matters: Common allergens. Some species produce mycotoxins, and Aspergillus fumigatus can cause respiratory infection in people with weakened immune systems or lung disease. High indoor counts warrant investigation.

Appearance: Greenish-black, often slimy colonies. Dark, ellipsoidal spores cluster at the tip of the conidiophore.

Where it's found: Chronically wet, cellulose-rich materials — drywall, ceiling tiles, cardboard and wood that has stayed damp for days or longer.

Why it matters: It produces mycotoxins and is tied to water damage. Its heavy spores are not easily airborne unless disturbed, so surface sampling is often more informative than air sampling. Its presence signals a significant moisture problem.

Appearance: Large brown, club- or drumstick-shaped spores with both cross-walls and lengthwise walls (muriform), often in short chains.

Where it's found: Soil and plants outdoors; indoors in damp spots — showers, window frames and around leaks.

Why it matters: One of the most important airborne allergens, strongly linked to asthma and allergic rhinitis. Indoor growth usually indicates dampness.

Appearance: Small, varied spores released by mushrooms (basidiospores) and sac fungi (ascospores).

Where it's found: Predominantly outdoors; they enter buildings through normal air exchange and spike after rain.

Why it matters: Mostly a background outdoor signal rather than a sign of indoor growth. They are useful as a reference — which is why we always pair your indoor sample with a same-day outdoor one.

Appearance: Grey to olive perithecia (flask-shaped fruiting bodies) covered in wavy hairs. The spores are lemon-shaped, olive-brown and single-celled.

Where it's found: Chronically damp, cellulose-rich materials — wet drywall, wallpaper, and damp books and cardboard.

Why it matters: A reliable marker of long-standing water damage. It can produce mycotoxins, and its presence usually means moisture has been in place for a while.

Appearance: Dark brown, egg-shaped spores with cross- and lengthwise walls (muriform), borne on a zig-zag conidiophore.

Where it's found: Very wet materials — water-damaged drywall, paint, textiles and window frames.

Why it matters: Needs plenty of moisture to grow, so indoors it points to a real water problem. Its spores resemble Alternaria and Stemphylium under the microscope.

Appearance: Slender, curved canoe- or sickle-shaped spores (macroconidia) with several cross-walls, plus tiny oval microconidia.

Where it's found: Very wet materials — around plumbing, humidifiers, drains and water-damaged building materials; also plants and soil.

Why it matters: An allergen; some species produce mycotoxins and can infect people with weakened immunity. Indoors it signals persistent wet conditions.