What mold is most common in Indiana homes?

The everyday molds

Most mold reports from Indiana homes include some mix of the same few groups. Their spores are everywhere outdoors, so finding them indoors isn’t a problem on its own. What matters is how much, and where.

Mold	Where we tend to find it indoors	What it usually tells us
Cladosporium	Window sills, bathroom caulk, HVAC coils, the back of furniture on cold walls	Condensation and surface moisture, very common in winter
Penicillium	Damp drywall, carpet, stored boxes, basements	Moisture that has lasted a while; often behind a musty smell
Aspergillus	Dust, HVAC systems, damp building materials	Indoor growth when counts or dust levels run well above outdoors
Alternaria	Near windows and doors, damp carpet	Often outdoor air coming in, sometimes indoor growth after water damage

Penicillium and Aspergillus spores look alike under a microscope, so air sample reports often group them together. In a summer basement or a damp crawlspace, that group is often the one that stands out.

Outdoor levels of these same molds climb through Indiana’s humid summers and into fall, then drop after a hard freeze. That’s why an indoor count means little on its own. It has to be read next to an outdoor sample taken the same day, in the same weather.

The water-damage molds

Two molds get our attention whenever they appear indoors because they need material that has stayed wet for a long time. Stachybotrys chartarum, the greenish-black mold most people mean by “black mold,” grows on paper-faced drywall, ceiling tile and wood after long-term leaks or flooding. Chaetomium grows in similar places and is common after slow leaks behind walls and under floors. Our page on Chaetomium mold covers it in more detail.

Their spores are heavy and sticky, so they don’t float far. A few in an air sample can point to a larger hidden source, which is why we pair air testing with dust and surface samples.

Where each tends to show up in an Indiana house

• Basements. Penicillium and Aspergillus on drywall, carpet and stored belongings during humid summers. Stachybotrys behind finished walls after a seepage or sump problem.
• Crawlspaces. Growth on joists and subfloor from humid vent air, often white or fuzzy. See whether white mold is dangerous.
• Attics. Dark staining on the roof deck from winter condensation, frequently Cladosporium or other common types.
• Bathrooms and windows. Cladosporium and other surface molds wherever water condenses daily.
• HVAC systems. Growth on wet cooling coils and drain pans, which the system can spread through the house.

Why the name matters less than the pattern

People often want to know if their mold is “the dangerous kind.” A better question is whether the house has a moisture problem that lets mold grow indoors. A lab report answers it by comparing indoor samples with outdoor ones. When indoor counts run well above outdoors, or when types rare in outdoor air show up inside, something is growing in the building, whatever its name.

Species does matter for one reason: some molds can produce mycotoxins. Stachybotrys can produce trichothecenes, and some species of Aspergillus and Penicillium can produce toxins such as ochratoxin A. Not every colony does, and the toxins can remain after the mold is dead. That’s why, for families with health concerns, we add mycotoxin testing in Indiana to standard mold testing.

We remove mold and mycotoxins from buildings. We don’t diagnose or treat medical conditions. If you have symptoms, please work with a doctor. With your permission, we’re glad to share test results and our plan with them.