Common Indoor Mold Species

Why Species Identification Usually Doesn't Matter

Before diving into specific molds, an important point: the CDC explicitly states they do not recommend mold testing for health purposes, and the EPA says if you see or smell mold, you should clean it up regardless of type.

Species identification rarely changes what you need to do: fix the moisture source and remediate properly. For guidance on proper remediation approaches, see our remediation guide.

That said, understanding common molds can help you communicate with professionals, understand test results if you have them (see our guide on how to read results), and recognize that the mold in your home is likely something common rather than unusual.

All of these molds require the same basic approach: control moisture and remove the growth.

Penicillium

Penicillium is another extremely common indoor mold genus, with hundreds of species. It is perhaps best known as the source of the antibiotic penicillin (P. chrysogenum).

Appearance is typically blue-green to gray-green with a velvety or powdery texture. The name comes from the Latin for "brush," referring to the brush-like structure of its spore-bearing structures.

Where it grows: wallpaper, wallpaper glue, carpet, water-damaged building materials, food (especially bread, cheese, and fruit), and HVAC systems. It spreads rapidly and produces a characteristic musty odor. If you smell mold but cannot see it, our guide on musty smell without visible mold can help.

Health considerations: Penicillium species are significant allergens and can trigger respiratory symptoms in sensitive individuals. Some species produce mycotoxins, though as discussed in our mycotoxins guide, the health significance of indoor mycotoxin exposure remains debated.

Common species include P. chrysogenum, P. expansum, and P. digitatum.

Stachybotrys chartarum ("Black Mold")

Stachybotrys chartarum is the mold most often referred to as "black mold" or "toxic black mold," though many molds can appear black. For a complete discussion, see our black mold facts page. It has received outsized attention compared to how often it is found in typical homes and what is known about health effects.

Appearance is black or dark greenish-black with a slimy, wet texture when actively growing. When dry, it becomes powdery. It often grows more slowly than many other molds.

Where it grows: it prefers high-cellulose, low-nitrogen materials such as drywall paper, ceiling tiles, cardboard, paper, and wood products. It requires significant, sustained moisture (chronic water damage) rather than brief wetness. This is why rapid response to leaks is so important.

Why the "toxic" reputation: Stachybotrys can produce mycotoxins called satratoxins. Media coverage in the 1990s and 2000s amplified fears. However, as discussed in our mycotoxins guide, the evidence for systemic toxicity from indoor Stachybotrys exposure remains controversial.

Health considerations: Like all molds, Stachybotrys can trigger allergic reactions and respiratory symptoms. Its spores are large and sticky, making them less easily airborne than some other molds. The CDC treats it the same as any other mold from a remediation standpoint. See our remediation guide.

Chaetomium

Chaetomium is a common water damage indicator that thrives on wet cellulose materials, similar to Stachybotrys. Its presence often indicates chronic moisture problems. Consider professional assessment for larger areas or repeated issues.

Appearance starts white or gray and darkens to brown or olive-green with age. It has a distinctive musty or earthy odor. If you notice this smell but cannot see mold, see our guide on hidden mold.

Where it grows: drywall, wallpaper, cardboard, wood, and other cellulose materials with chronic water damage. Often found alongside or instead of Stachybotrys in water-damaged buildings, particularly in basements and areas with ongoing leaks.

Health considerations: Like other molds, Chaetomium produces allergens and can cause respiratory symptoms. Some species produce mycotoxins. It is less studied than some other indoor molds but follows the same remediation principles.

Official Resources