There are thousands of mold species, but only a handful show up regularly inside homes. Knowing the common types of mold, what they look like and where they grow can help you spot a problem early. The bottom line, though, is the same for every species: if mold is growing indoors, there is a moisture problem, and both the mold and the moisture need to be fixed.
Why Mold Grows Indoors
Mold spores are everywhere, indoors and out. They only become a problem when they land on a surface with moisture and an organic food source like drywall paper, wood, carpet backing or dust. Leaks, flooding, high humidity and condensation are the usual triggers. That is why mold so often follows water damage.
The 10 Most Common Types of Household Mold
1. Aspergillus
One of the most common indoor molds. It appears in many colors, often green, yellow, gray or black, and grows on walls, insulation, dust and damp building materials. Some species can cause respiratory issues, especially in people with weakened immune systems or lung conditions.
2. Cladosporium
Usually olive green, brown or black with a velvety or powdery texture. It grows on fabrics, carpets, wood, window sills and the back of toilets, and it can grow in cooler areas. It is a common allergen.
3. Penicillium
Typically blue or green and fuzzy. It spreads quickly and is often found on water-damaged drywall, carpet, wallpaper and insulation. It is known for a strong musty odor.
4. Alternaria
Dark green or brown with a fuzzy texture. It loves damp areas such as showers, bathtubs, under sinks and around leaky windows. It is one of the most common allergy-related molds.
5. Stachybotrys chartarum (“Black Mold”)
Dark greenish-black and often slimy when wet. It needs constant moisture and grows on cellulose-rich materials like drywall, ceiling tiles and wood after prolonged leaks or flooding. Read our full guide on black mold signs, health risks and removal.
6. Chaetomium
Starts white or gray and darkens over time, with a cotton-like texture. It is commonly found on drywall, wallpaper and baseboards after water damage and has a distinctly musty smell.
7. Fusarium
Pink, white or reddish. It can grow in cooler temperatures and is found on water-damaged carpet, wallpaper and fabrics.
8. Mucor
White or gray and fast-growing in thick patches. It is often found near HVAC systems, ducts and condensation-prone areas, and on damp carpet.
9. Trichoderma
White with green patches and a wooly texture. It grows on damp wood, wallpaper, carpet and other wet surfaces and can damage building materials.
10. Aureobasidium
Pink, brown or black, and often turns darker with age. It is common on painted or wooden surfaces, window frames and caulking.
Can You Identify Mold Type by Color?
Not reliably. Many species change color as they age or depending on the surface they grow on, and several types can look nearly identical. The only way to confirm species is lab analysis. For most homeowners, though, the species matters less than the size of the growth and the moisture source behind it. The CDC and EPA both recommend treating all indoor mold growth the same way: remove it and fix the moisture.
Is It Mold or Mildew?
Mildew is a surface-level type of mold that stays flat and powdery, usually on bathroom tile or window sills. Learn the difference in mold vs. mildew: how to tell them apart.
When to Call a Mold Remediation Professional
The EPA suggests that homeowners can usually clean small areas of mold (less than about 10 square feet) themselves. Call a professional if:
- The affected area is larger than 10 square feet
- The mold followed a flood, sewage backup or contaminated water
- Mold is inside HVAC systems or ductwork
- You smell mold but cannot find it, which suggests growth inside walls or under floors
- Anyone in the home has asthma, allergies or a weakened immune system
Types of Mold FAQ
Which type of mold is the most dangerous?
Any mold can cause problems for sensitive people. Stachybotrys gets the most attention, but Aspergillus and others can also affect health. Size and location of growth matter more than species.
Does mold testing tell me what type I have?
Yes. Air and surface samples analyzed by a lab can identify mold genera. Testing is most useful when mold is suspected but not visible, or to confirm a remediation was successful.
Will bleach kill mold?
Bleach can whiten mold on non-porous surfaces, but it does not penetrate porous materials like drywall or wood, and it does not fix the moisture problem. Professional remediation removes the contaminated material instead.
Need Help Now? Longview Restoration Is Available 24/7
Longview Restoration is a locally owned, IICRC-certified water, fire, mold and storm damage restoration company. Our technicians respond day or night, document everything for your insurance claim, and restore your property to preliminary condition.
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