MoldHelpUSA
There are thousands of mold species, but only a handful turn up in most homes. According to the CDC, as summarized by the National Institute of Environmental Health Sciences, the most common indoor molds are Cladosporium, Penicillium, Aspergillus, Alternaria, and Stachybotrys chartarum, the one usually called black mold.
Knowing their names is interesting, but it changes less than people expect. The CDC's guidance is that it is not necessary to determine what type of mold you have, because all molds should be treated the same with respect to health risks and removal. This guide describes the common types, what they tend to look like, and when identifying the species is worth it.
The most common indoor molds
| Mold | Typical color | Often found indoors on | Notes |
|---|---|---|---|
| Cladosporium | Olive-green, brown, or black | Painted surfaces, window frames, bathroom surfaces, fabrics, air conditioning components | Very common outdoors; a frequent allergen |
| Penicillium | Blue-green or green, often fuzzy | Water-damaged drywall, wallpaper, carpet, insulation; also food | Common after leaks; a frequent allergen |
| Aspergillus | Green, yellow, white, or black, depending on species | Dust, walls, air conditioning systems, stored materials | Some species can cause lung infections in people with weakened immune systems |
| Alternaria | Dark green, brown, or black | Damp window frames, showers, areas near leaks; common outdoors on plants | A well-known allergen linked to asthma symptoms |
| Stachybotrys chartarum | Greenish-black | Drywall paper, ceiling tiles, wood, and paper that stay wet | Needs constant moisture; often called black mold |
Lab reports from water-damaged homes also commonly list other molds, such as Chaetomium, Trichoderma, and Mucor. The same rules apply to all of them.
Mold by color
People usually describe mold by color, but color is a weak guide:
- Black or dark green: many species, including Cladosporium, Alternaria, some Aspergillus, and Stachybotrys. Dark does not mean Stachybotrys. See what black mold looks like.
- Green or blue-green: often Penicillium or Aspergillus, but not always.
- White: many molds start white or stay white on certain materials. On concrete or block, check whether it is efflorescence, a crusty salt deposit that dissolves in water.
- Yellow or orange: several molds, and some slime molds outdoors.
- Pink or red: in bathrooms, pink film is often a bacterium feeding on soap residue rather than a mold.
Color can change with age, moisture, and the material underneath. The EPA's reminder applies: mold comes in many colors, not just black.
Allergenic, pathogenic, and toxigenic
You will often see molds sorted into three groups:
- Allergenic: can cause allergic reactions and asthma symptoms in sensitive people. Most common indoor molds fall here.
- Pathogenic: can cause infections, mostly in people with weakened immune systems or chronic lung disease.
- Toxigenic: can produce mycotoxins under certain conditions.
These groups overlap, and the same mold can fit more than one. The CDC says the hazards of molds that may produce toxins should be considered the same as other common molds, and it considers the popular term "toxic mold" inaccurate. None of these labels changes how the mold is removed.
Types of mold in basements and crawl spaces
Basements and crawl spaces often show Penicillium, Aspergillus, and Cladosporium, along with white molds on wood framing and Stachybotrys where drywall or paper has stayed wet. Crawl space framing commonly shows white, black, green, or yellow growth. The approach is the same regardless of type: fix the moisture and remove the growth. See mold in the basement and mold in the crawl space.
Which types of mold are dangerous?
Any indoor mold can cause health problems for some people. The CDC lists a stuffy nose, sore throat, coughing or wheezing, burning eyes, and skin rash, with more severe reactions possible in people with asthma or mold allergies and lung infections possible in people with weakened immune systems or chronic lung disease. The type of mold matters less than how much there is, how long people are exposed, and how sensitive they are. See is black mold dangerous? If anyone has symptoms, talk to a doctor.
Do you need to identify the type?
For most homes, no. The EPA says that in most cases, if mold growth is visible, sampling is unnecessary, and no federal limits exist for mold or mold spores. Identification can still be useful:
- When a doctor asks about exposure for a specific medical reason
- For an insurance claim, a legal dispute, or a home sale that needs documentation
- To look for hidden growth when there is a smell but nothing visible
- To confirm that remediation worked, using clearance samples
Only a lab can identify mold, from a tape, swab, bulk, or air sample. See what a mold inspection involves and our mold testing page.
What to do, whatever the type
- Find and fix the moisture source.
- Clean small areas on hard surfaces with detergent and water, wearing gloves, goggles, and an N-95 respirator.
- Remove porous materials with mold growth, such as drywall, ceiling tiles, and carpet.
- Call a professional for areas larger than about 10 square feet, hidden growth, or mold in the air conditioning system.
See DIY vs. professional mold removal.
Next step
If you own your home and the mold covers more than a small area or keeps coming back, call the number on this page to be connected with an independent local mold inspection or mold removal company.