Mold can be an absolute nightmare for families, but the reality is that every home has some degree of mold. It’s inevitable.1 As expert mold remediation specialist Rob Hopkins told The Washington Post recently:

“There’s never been a mold test that we’ve done that didn’t have any mold. Every house, every environment has mold spores.”

We know: Yuck. It’s important to understand, though, that you’re never going to fully remove you or your family from mold exposure, but 99 percent of your interaction with the stuff is far from dangerous. We’ll get into all that in a minute, but first, let’s review what you’re up against.

What Is Mold?

different types of mold

When we say mold, we’re actually referring to the fungal growth that appears on damp and decaying organic matter.2 There are tons of different types of mold, and they’re found both indoors and out during all seasons of the year. So “mold” is an umbrella term for various different types of fungi you’ll find growing literally everywhere.

The Good News About Mold

While it can be a headache to deal with when it’s inside your home, mold actually serves a really important function in natural life cycles. Outdoor mold breaks down materials. Without it, we’d be up to our necks in fallen trees, leaves, and other organic debris. Thanks, mold!

FYI: Mold has been around much longer than plants. The first land fungi evolved about 1 billion years ago, with plants showing up around 700 million years ago.3

With that in mind, in order to grow, mold needs three conditions: a suitable temperature, “food” to “eat,” and a source of moisture. Eliminating one of the three will eliminate your mold.

The Bad News About Mold

Now here’s the bad news. Mold feeds on organic matter. That means dirt, dust, dead skin cells, pet hair – you know, all the stuff that’s virtually impossible to eliminate from your house — especially if you have little ones running around. Heck, even the building materials your house was constructed from are the favorite meals of molds.

The temperatures at which molds thrive also just so happen to be the temperatures at which humans feel the most comfortable, so that’s no good either if you’re looking to mitigate a mold problem. That just leaves the final factor: moisture.

Removing sources of moisture is the best way to prevent mold from harming your family or damaging your home, but mold doesn’t need soaked floorboards or burst pipes to thrive in your home. Really all it needs is a relative humidity that’s above 60 percent.4

Expert Tip:: We recommend investing in a good dehumidifier and setting it below 50 for mold-prone parts of your house.

So now that you understand what mold is, let’s take a closer look at the types of mold that might show up in your home.

Understanding the Three Different Types of Mold

Mold can be classified into three categories of ascending threat: allergenic, pathogenic, and toxic. Let’s take a look at each.

1. Allergenic Mold

Depending on your sensitivity to mold spores, some of the most common types of household mold — the allergenic ones — might cause watery eyes, sneezing, and coughing. They might also cause rashes or other minor symptoms. They might also do absolutely nothing; it all depends on your individual reaction.5  An example of an allergenic mold is Penicillium, the green stuff you find growing on the garlic bread you left in the takeout box for too long.

Allergenic Mold Breakdown:

  • Threat Level: Low to moderate
  • Prevalence: Very common in most homes
  • Symptoms: Mild allergies, sore throat, watery eyes, skin irritation
  • Examples: Alternaria, Aspergillus, Cladosporium
Cladosporium spp

Cladosporium mold

2. Pathogenic Mold

More severe reactions occur when pathogenic molds are present and in large quantities, especially if a person is immunocompromised. The line is kind of blurry between pathogenic and allergenic molds, as reactions have everything to do with quantity and sensitivity.

Complicating matters further, some types of molds that are considered allergenic have certain strains that are considered pathogenic. What does that mean? It means that whenever you see mold, you should be cautious, especially if you’re living with eldery relatives or have small children.

Pathogenic Mold Breakdown:

  • Threat Level: Moderate to high
  • Prevalence: Common in certain types of homes and climates, but nowhere near as common as allergenic molds
  • Symptoms: Moderate to severe allergic reactions, shortness of breath, heavy coughing
  • Examples: Cryptococcus neoformans, Aspergillus species (A. fumigatus and A. flavus), Histoplasma capsulatum

An example of pathogenic mold is Cryptococcus neoformans. This mold can be found growing on damp building materials and in rare cases can cause cryptococcal meningitis.

3. Toxigenic Mold

The final category — toxigenic mold — is harmful to all humans and animals that encounter it. These are obviously the ones you really want to protect your family from, and the ones that will require professionals to mitigate and remove from your home. The notorious black mold, for instance, is a toxigenic mold that can cause respiratory failure, especially among those who are high-risk.

Toxigenic Mold Breakdown

  • Threat Level: High to extreme
  • Prevalence: Fairly rare, typically appearing only when mold outbreaks have gotten out of control
  • Symptoms: Can cause severe reactions, including respiratory distress and failure
  • Examples: Aspergillus species (A. versicolor, A. niger, and A. flavus), Stachybotrys chartarum, more commonly known as “black mold”

The Most Common Types of Household Mold

According to the CDC, the three most common types of indoor molds are Cladosporium, Penicillium, and Aspergillus. None of these are really threatening to otherwise healthy people in small quantities, and it’s likely that you’re breathing in these spores as you’re reading this article. We know, we know: Yuck.

Pro Tip: Your standard homeowners insurance policy isn’t going to protect you from damage caused by mold, nor will it pay for its removal and mitigation. For that, you’re going to need a special rider. Read up on our guide to mold insurance for more information.

With that in mind, though, there are actually 11 common molds that you need to be aware of.7 Note, though, that mold’s color and presentation depend almost entirely on the materials it’s growing on, so if it’s really important for you to identify the type of mold you’re seeing — like if your child is exhibiting unexplained respiratory problems — you’re likely going to have to call in an expert. Now let’s take a look at them.

Editor’s Note: You’ll notice the “appearance” field goes away on some of the pathogenic and toxigenic molds in this list. That’s because those specific molds have to be identified under a microscope, not with the naked eye.

The 11 Common Types of Household Mold

Name: Alternaria
Categorization: Allergenic
Appearance: May present as dark gray spots
Found on: If the materials are damp, Alternaria can be found growing on wood, iron, tiles, brick, plaster, wallpaper, paper, and canvas.
Danger: Hardly any

Name: Aspergillus
Categorization: Allergenic
Appearance: Black on the surface and white or yellow-ish underneath
Found on: Dead leaves, soil, grain; think houseplants and crawl spaces
Danger: Barely any

Name: Cladosporium
Categorization: Allergenic
Appearance: Brown, green, or black spots
Found On: Mostly occurs on damp building materials like gypsum board, acrylic painted walls, wood, wallpaper, carpet, insulation, and cooling units
Danger: Barely any

Name: Penicillium
Categorization: Allergenic
Appearance: Blue-green, fluffy outcroppings
Found On: Mostly food
Danger: Barely any

Penicillium mold

Penicillium mold

FYI: Penicillium is a genus that includes hundreds of species, some of which can be used to make the popular antibiotic penicillin.8

Name: Aspergillus species (A. fumigatus and A. flavus)
Categorization: Pathogenic
Found On: Damp building materials
Danger: Moderate; might cause chronic pulmonary infections in at-risk individuals

Name: Cryptococcus neoformans
Categorization: Pathogenic
Found On: Damp building materials
Danger: Moderate; might further weaken the immune system of immunocompromised people or, in rare cases, cause cryptococcal meningitis

Cryptococcus neoformans mold

Cryptococcus neoformans mold

Name: Histoplasma capsulatum
Categorization: Pathogenic
Found On: Soil, especially soil mixed with bird and bat droppings
Danger: Moderate; dangerous levels of spores can be released during construction projects and may cause pulmonary histoplasmosis

pulmonary histoplasmosis in chest

Pulmonary histoplasmosis in chest

Name: Fusarium, species (F. solani, F. oxysporum, and F. moniliforme)
Categorization: Toxigenic
Found On: Damp drywall, carpets, wood, and flooring, as well as soil
Danger: Moderate; even in healthy people, specific Fusarium molds like the ones listed above can cause skin, nail, and eye infections

Name: Penicillium species (P. brevicompactum, P. chrysogenum, P. citrinum, P. corylophilum, P. cyclopium, P. expansum. P. fellutanum, P. spinulosum, and P. viridicatum)
Categorization: Toxigenic
Found On: Foods
Danger: Very high; the toxic varieties of Penicillium molds are most dangerous when ingested; they can also cause acute symptoms when inhaled; while the science is still unconfirmed, it’s strongly suspected toxic Penicillium can cause convulsions, paralysis, cardiovascular damage, and respiratory arrest.9

Penicillium mold on bread

Penicillium mold on bread

Name: Aspergillus species (A. versicolor, A. niger, and A. flavus)
Categorization: Toxigenic
Found On: Damp areas and building materials
Danger: Very high; diarrhea, upset stomach, and respiratory distress, including aspergillosis, where the mold can form a hyphal ball (fungus ball) in the lungs and extrude allergens and toxins into the bloodstream.10

Name: Stachybotrys chartarum, more commonly known as “black mold”
Categorization: Toxigenic
Appearance: Circular-shaped spots that are black, dark green, or dark brown and furry in appearance; might have flecks of white or orange
Found On: Damp areas with lots of cellulose, like cardboard or paper items
Danger: High; can cause respiratory distress, mycotoxins are harmful if consumed

Black mold on ceiling

Black mold on ceiling

While few household molds are toxigenic, any significant mold outbreak can cause health problems for you, your family, and your children, and it can cause serious damage to your home. Simply stated, if you see mold, get rid of it.

How to Remove Mold

Just like every household is different, every mold outbreak is different. But here’s what to do if you find mold in your home.

First, you’re going to want to get rid of the mold itself. Sometimes this is as simple as wiping your shower tiles with a mild cleaner, but sometimes it’ll be more involved. For major outbreaks, you’re always going to want to call in the experts. It’s very difficult to tell if a mold is dangerous just by looking at it, so it’s better to be safe than sorry.

If you are going to tackle the project on your own, make sure you wear nose and mouth protection. An N95 mask or particulate respirator is recommended. Make sure you wear clothing that covers your arms and legs, and wear gloves to protect yourself from contact with the mold itself.

Ventilate the area as best you can, and — if possible — use an air purifier while you work to remove spores from the environment. Remove and discard any moldy material you find, and clean it off surfaces using a commercial mold remover or a diluted bleach mixture. Diluted ammonia can also work.

Pro Tip: Be careful working with chemical cleaners, as their fumes can become overwhelming. And never, ever mix ammonia and bleach. The mixture can literally kill you.

Once that’s done, do your best to make sure the mold doesn’t return. Fix any sources of moisture, like leaky fixtures or spillover fans, or, as mentioned above, invest in a dehumidifier. Remember, moisture is your No. 1 enemy when it comes to preventing mold.

Final Thoughts on Household Mold

Like we said at the top of this guide, there’s no way you’re ever going to isolate yourself or your family from mold completely; it’s just too pervasive in our environments. However, that doesn’t mean that you should be lackadaisical when it comes to mold in your home. If you notice it, remove it, or else it can snowball out of control.

While most molds are kinda gross, they’re relatively harmless. You don’t need to freak out if you see dark spots under your sink or in your crawlspace. Simple mitigation techniques like the ones listed above will likely take care of the problem. That said, for bigger outbreaks or if you’re noticing inexplicable allergies or respiratory issues, you should test your home for mold.

And finally, if dangerous mold is found in your home, or if you discover an area that has a large mold colony growing on it, you’ll need to call in the professionals.

Household Mold FAQs

Is mold dangerous?

The vast majority of household molds are perfectly safe in small quantities. That said, some forms of common molds can become pathogenic or toxic in larger amounts.

What does black mold look like?

The infamous black mold grows in damp areas with lots of cellulose. Think wallpaper, cardboard, and paper products. It presents as black, dark brown, or dark green fuzzy circles of varying sizes that sometimes have white or orange flakes.

Can I clean mold myself?

Most molds can be easily mitigated with simple household products, but for larger outbreaks, you’ll need to take precautions for removal or call in professionals.

How do I know if my house has mold?

The most obvious way of figuring out if you have mold is to go looking for it. Check in moist, warm areas, like under sinks, behind toilets, and near your air condition unit. A musty smell is also a good indicator mold might be lurking somewhere.

How much is mold cleaning?

Each situation is unique, of course, but expect to pay between $13.33 and $28.33 per square foot. Small projects have an average cost of $458 while larger jobs cost around $6,333.