Most Common Types of Mold in the Home

Spotting a fleck of mold on your sandwich? Not the best feeling. But spotting mold in your home? Well, that’s even worse. After all, unlike with the sandwich, you can’t just solve that problem by tossing it into the garbage and going out for a new BLT. 

As distressing as it can be to encounter a suspicious patch of spots or spores in your home, it’s not the end of the world, and it’s extremely common. Mold tends to be pretty comfortable making itself at home almost anywhere—indoors and outdoors, cold regions and warm climates, in large buildings and small households—as long as moisture levels are high. 

To get a clear picture of the kinds of molds that are most frequently found in homes—and possibly reveal what may be lurking underneath your basement carpet—check out our guide to the most common types of house mold and how they can be removed with the proper insulation removal services.

Mold: What You Need to Know

A fungus that multiplies by spreading its spores in the air, mold announces its presence through sight (in a range of colorful and dismal blotches) and smell (musty, earthy, stale—like a pair of wet socks in a forest of rotting trees). It thrives in damp environments and grows on organic substances like:1

  • Paper
  • Wood
  • Soil
  • Fabric

Left to run wild, mold can degrade the very integrity and appearance of your home—rotting your drywall, damaging your hardwood floors, and leaving stains and splotches on your walls and carpets.1 

The 3 Types of Mold

Smelly, ugly, and destabilizing? It’s safe to say that all mold inspires annoyance and aggravation. But not all mold poses the same risks to your home, or you. To understand how different molds might differ in their behavior and impact, let’s consider the three main mold categories:

  1. Allergenic – In large quantities, allergenic molds may provoke mild allergic responses in people with mold sensitivitie.2 However, they’re unlikely to cause illness or infection in smaller quantities, or in populations without mold allergies. . 
  2. Pathogenic – These kinds of mold can cause infection in people and animals, presenting a more serious risk to immunocompromised individuals.2
  3. Toxigenic – Toxigenic molds produce “mycotoxins”—toxins that have been connected to serious health problems like pulmonary hemorrhage, cancers, and neurological disorders.3 

Common Household Molds

Experts estimate that there are nearly 300,000 kinds of mold in the world.5 But there are a few usual suspects that tend to invade homes more frequently than others. Being proactive is the best way to prevent mold in your crawl space or attic. 

If you suspect that you have some fungus among…your things, it pays off to know what you’re dealing with so that you can take appropriate measures. While some species of household molds are relatively innocuous, a certain few may compel you to call in the big guns.  

To keep you in the know, we’ll unpack the most common molds you may encounter squatting in your home. Plus, how to kick them to the curb. 

1. Aspergillus

With hundreds of subspecies, Aspergillus molds proliferate in all sorts of climates and regions and can be commonly found indoors in hospitals and homes.6 While a little over 1 out of ten subspecies of aspergillus are considered pathogenic and dangerous for humans, the vast majority simply pose allergenic risks.

Still, if you’re immunocompromised or have any preexisting respiratory issues like asthma, breathing in the fungal spores can be harmful and lead to infection.3 Aspergillus may be common, but that doesn’t mean that you want to live with it.

Here’s what else you need to know about aspergillus:

  • It’s everywhere – Aspergillus spores are so widespread indoors and out that it’s probably impossible to avoid exposure to them throughout your life. For folks with healthy immune systems, breathing in the spores likely will not lead to any health issues.
  • Maybe even on your sandwich – Somespecies of aspergillus proliferate in carbon-rich environments like compost piles and rotting plants, but the mold also commonly seeks sustenance in starches.7 Just like a marathon runner before the big race, Aspergillus never turns down an opportunity to carbo-load—thriving on slices of bread and potatoes.
  • It can be colorful – Aspergillus patches usually appear white at the beginning. Then, depending on the subspecies, the mold can turn green, black, yellow, or reddish-brown.

2. Alternaria

Alternaria is famous for wreaking serious havoc on plant life. But this fungus can also negatively impact your home—and your health.

A common allergen, Alternaria presents with dark gray spots and can provoke allergic reactions including8:

  • Runny noses
  • Red, watery eyes
  • Throat irritation 

What’s more, research supports that exposure to the mold is a powerful indicator of respiratory diseases and a common risk factor for asthma.9

While folks are likely to encounter Alternaria outdoors—as we mentioned above, it’s ubiquitous in nature, likely even to blame for 20 percent of agricultural plant loss10—it can also invade the home. In fact, the National Survey of Lead and Allergens in Housing found one species of Alternaria in 95 to 99 percent of the dust samples collected in households nationwide.10 

Alternaria grows on damp surfaces and tends to lurk in places that see a lot of moisture, including:

  • Showers
  • Sinks
  • Air-conditioning units
  • Wet wooden areas, like window frames or floors

3. Cladosporium

More than 500 subspecies comprise Cladosporium, a fungus that lives in cold climates and warm regions, indoors and outdoors.12 Like Aspergillus and Alternia, Cladosporium is allergenic and can cause those pesky cold-like symptoms in folks with sensitivities.

Cladosporium can appear as brown, green, or black spots and can oftentimes be found “peppering” damp, wet areas that may include:12

  • Window sills
  • Toilet lids
  • Attics
  • Air-conditioning units
  • Carpets
  • Curtains
  • Air ducts

4. Penicillium

Penicillium is here to remind us that molds—like people—can be complicated. In fact, sometimes they can even be downright useful.

The natural source of the antibiotic penicillin, Penicillium’s bacteria-fighting power has undoubtedly saved lives and made incredible strides toward medical, and human, advancement.14 Which is not to say that Penicillium is all brains and no fun. Some species can also be used to cure meats and make cheeses.15 

Unfortunately for homeowners, Penicillium’s overachieving nature also extends to its ability to spread rapidly, and without much support. While Penicillium depends on moisture to grow, like all molds, it’s relatively low-maintenance—able to survive, and even thrive, in low-humidity environments.16 

That means that many, even those without water damage, can be vulnerable to a Penicillium invasion. All it takes is one damp spot, or one tempting meal. Penicillium loves to munch on spoiling food like bread and fruits, as well as cellulose-rich household materials, including:

  • Carpets
  • Upholstery
  • Cardboard boxes
  • Plant debris

While it may look remarkable thanks to its striking blue-green and yellow patches, these fuzzy spores are not your friend. Penicillium infestations can aggravate allergic responses in sensitive populations, while some species are even toxigenic for humans and animals—releasing harmful mycotoxins that can cause severe infection and disease if inhaled or consumed.15

5. Stachybotrys (black mold)

If the phrase “black mold” raises your hackles, you aren’t alone. For many homeowners, the term summons anxiety and fear—carrying associations with toxicity, disease, and danger. But what is this fearsome fungus? And how can you recognize it?

Black mold is simply the colloquial term for Stachybotrys, a fungus that grows indoors on cellulose-rich materials that can include:13

  • Cotton
  • Drywall
  • Lumber
  • Dust
  • Lint

Stachybotrys flourishes in wet conditions—say, after a flood or a leak—and reveals itself through its heavy, musty odor and a tell-tale greenish-black appearance.22 

Black mold earns its serious reputation thanks to its status as a toxigenic mold, which means that its spores produce mycotoxins that can cause harm to humans when inhaled. It’s worth noting, however, that Stachybortyrs, like all molds, generally only releases spores when it’s disturbed.13 

So, if you find a suspicious patch of mold in your home, don’t panic (or hold your breath forever). Simply take some distance, cease any loud, disruptive movements or construction, and call a professional.

Show Mold the Door with Attic Construction

But sometimes what’s more devastating is the mold that we don’t see—the mold that’s hiding in our attics and crawl spaces. Could that be what’s behind the endless allergies, the musty smells you can’t quite pin down? 

If you’ve experienced a leaky roof or water damage, fungi may have found a fruitful existence in your attic. 

We’re here to show it the door. At Attic Construction, our experienced technicians use effective, innovative equipment to decontaminate your spaces from any intruders, whether they’re rodents, germs, or mold. Plus, our skilled team will work tirelessly to remove odor and harmful bacteria so that you can take a much-needed deep breath, assured that your home is protected and safe. If you suspect a rodent has found its way into your home, learn how to spot rodent entry points and when to call in a professional. Once your attic is cleaned up from any molds or rodents, we can provide top quality insulation installation & crawl space cleaning services for when you’re ready to take your attic to the next level. 

Ready to turn your mold news into old news? Call Attic Construction today. 

Have you ever wondered if attic insulation is actually sound proof? Find the answer to this question and more here in our latest blog.


  1.  EPA. Mold Course Chapter 1: Introduction to Molds.
  2. Inspectapedia. Mold Classes & Classes of Mold-Related Illness.
  3. CDC. Basic Facts About Mold and Dampness.
  4. The Asthma & Allergy Center. Is It Mold or a Cold?
  5. Medical News Today. Is mold in your house a problem? What you need to know.
  6. NCBI. Aspergillus species in indoor environments and their possible occupational and public health hazards.
  7. Family Handyman. What to Know About Aspergillus Mold.
  8. Mayo Clinic. Mold Allergy.
  9. ScienceDirect. Alternaria alternata allergens: markers of exposure, phylogeny, and risk of fungi-induced respiratory allergy.
  10. NCBI. Dustborne Alternaria alternata antigens in U.S. homes: Results from the National Survey of Lead and Allergens in Housing.
  11. Mold Busters. Alternaria.
  12. Healthline. What is Cladosporium?
  13. SFGate. How to Tell if Black Mold Is Hiding in Your Walls.
  14. NIH. How Did They Make Penicillin?
  15. Indoor Doctor. Hidden Risks: Penicillium Mold in the Indoor Environment.
  16. Family Handyman. What to Know About Penicillium Mold.

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