Learn what mold is, how to identify it, where it lives, and what you should do about it
Maybe you’ve seen it growing on your grout in the bathroom, or on a slice of pizza you left in the fridge for too long. It might be growing on the storage boxes in your garage, or slowly creeping into your crawl space. We’re all relatively familiar with mold, but do we really understand what it is and what to do when we find it in our homes?
We’re going to explain all of that and more. But before we can talk about the types of mold, how to get rid of it, and how to prevent it from returning, we need to first understand mold at a basic level.
FYI: There are about 100,000 identified species of mold out there, but scientists estimate the actual number could be as high as 300,000.1 The vast majority of these molds are harmless, but there are some you need to watch out for.
Mold is the common name given to the numerous different species of fungal growth that breaks down damp organic material.2 They can appear in many different ways, but they are generally slimy or fuzzy and can have black, gray, white, orange, green, brown, blue, or purple-ish colorations.
In nature, mold has quite a few benefits.3 These include:
There are drawbacks, though, when mold leaves nature and comes indoors.4 These can include:
Now that we understand what mold is, what it’s good for, and some of its risk factors inside the home, we can take a look at arguably the most important question in any discussion of mold.
Pro Tip: If you’re buying a home, it’s fairly common that the inspection will reveal mold issues. To learn what you should do if this happens, check out our guide to purchasing a home with mold.
Let’s clear something up. The vast majority of mold, in small quantities, is not dangerous. It’s only when it’s present in large amounts that health risks become elevated, and only certain people will experience anything more than a mild annoyance.
That said, there are three classifications of mold — allergenic, pathogenic, and toxigenic, each with increasing risks of negative health outcomes to humans and animals. Unfortunately, it’s difficult to determine what type of mold is growing in your home just by looking at it. For that, you’ll need a professional test. With that in mind, though, a good rule of thumb is to treat a significant mold infestation in your home as a serious health concern.
Pro Tip: Remember, risk level is not so much determined by the type of mold you have growing in your home; it’s the extent of the contamination and how long you remain exposed to it.
And now a quick discussion about what might be the most infamous mold out there — Black Mold.
Toxic molds produce chemicals called mycotoxins, which are harmful — and potentially fatal — to people and animals. One specific variety of toxic mold is known as Stachybotrys chartarum, also known as the insidious black mold.5
But does it deserve its reputation? It’s true that Stachybotrys chartarum is toxic, but only if they are consumed. There’s no scientific link between inhaled black mold mycotoxins and deadly diseases, or symptoms like memory loss. In all, there’s no scientific reason to believe black mold is any more or less dangerous than its less-maligned relatives.6
Pro Tip: “Black” mold is just what it’s colloquially called. It can also be green or brown. Sometimes it’ll take on shades of orange or have flecks of white in it. Most of the time, it’s a little fuzzy in appearance.7
But again, exposure to any type of mold can have negative health outcomes for certain people, and it’s hard to know what kind of mold you’re dealing with. That means any mold contamination should be dealt with appropriately, especially if your family is at risk. How do you know if the threat mold poses is higher for your family, though?
In small amounts, mold shouldn’t be thought of as dangerous for healthy adults. Certain folks, though, need to be more cautious around it and be aware of the threats it can pose. Here’s a breakdown of populations with elevated risk levels when it comes to mold.8
With this in mind, let’s talk about some of the symptoms of mold allergies, and what can be done about them.
For most people, mold allergies are a minor to moderate annoyance.9 We have more information in our mold allergy guide, but symptoms might include:
For those super sensitive to mold exposure, though, symptoms can be more severe. These might include:
Most of the time, minor symptoms can be treated with over-the-counter antihistamines or decongestants. If your or your family member’s symptoms are more severe, persist, or worsen, you might need to call a doctor. If these major symptoms are indeed related to a mold allergy, action will need to be taken to improve the air quality of your home. Before we go there, though, we need to discuss some of the more severe reactions to mold and clear up some myths.
Before we talk about toxic mold syndrome, we need a bit of a history lesson.
Back in the 1990s, several children in Cleveland, Ohio, developed bleeding in the lungs, and one child passed away. A preliminary study indicated that exposure to black mold was a potential cause of the illness. However, on further review, the Centers for Disease Control and Prevention determined that the study was in error and that the cause of the death should remain unknown. However, the media ran with the story and the subsequent panic fueled fears over a so-called “toxic mold syndrome.”10
Let’s be clear — in scientific terms, toxic mold syndrome does not exist. It’s not a medical diagnosis, and there is no group of symptoms or physical findings associated with this “disease.” Very similar to toxic mold syndrome is something called “sick building syndrome,” which is recognized by the EPA.11 This syndrome is defined as “situations in which building occupants experience acute health and comfort effects that appear to be linked to time spent in a building, but no specific illness or cause can be identified.”
FYI: There is no known treatment for building sickness syndrome. Avoidance and elimination of the underlying causes of the problem are recommended, but generally speaking, treatments are aimed at managing symptoms.12
Most often these problems are linked to overall indoor air quality. While mold might play a factor in this complex syndrome, any other amount of air quality contaminants, including bacteria, plumbing exhaust, cleaning agent fumes, pesticides, among others, could be to blame.
That said, there are some serious disorders and diseases that can be caused by long-term exposure to mold. These are medically understood and confirmed to be the result of such exposure.
One of the most common diseases caused by mold exposure is called Aspergillosis, which can manifest in a few different ways,13 including:
Mold in a home can also foster the production of dangerous bacteria and other microbes. Exposure to these symbiotic agents can result in other health issues, including:
Now keep in mind, these conditions are relatively rare, and mostly occur in at-risk populations or in those with other comorbidities. Incidental exposure to common household mold will rarely result in major negative health outcomes for healthy individuals.
Still, it’s not a good idea to let mold grow in your home. It will certainly degrade the quality of your air, increase the risk of an allergic response, and could even damage your home to the tune of thousands of dollars. So let’s take a look at where mold typically grows.
Mold is quite literally everywhere, and most homes have some degree of mold in them.15 That’s because, unfortunately, our homes are excellent mold habitats. That’s because mold only needs four things to survive:16
And wouldn’t you know it, our houses check all of those boxes. The biggest factor in keeping your home mold-free is reducing moisture, but we’re going to get to that in a bit. First, here are some common places to check for household mold.17
A lot of mold contamination in homes is apparent and visible. This mold is usually surface level and can be handled by properly cleaning the affected area. However, you also want to be on the lookout for mold that might not be as apparent. Mold growth areas might include:
So now that we know where mold commonly grows, let’s talk about the types of mold you might encounter during your inspections.
We have a lot more on this in our guide to the most common types of household mold, but we’ll give you a quick summary. The most common types of indoor mold are Cladosporium, Penicillium, and Aspergillus.18 Here’s a breakdown of each:
These three molds are relatively harmless to families without sensitivities or underlying health concerns. But other, more dangerous types of mold that can be found in homes include:
Now keep in mind it’s almost impossible to tell with any certainty which type of mold you’re dealing with unless you have access to a lab and a degree in mycology. That’s why you should treat every significant mold contamination with some degree of caution. How exactly? We’ll take a look at that next.
Every instance of mold contamination is unique, but for the most part, molds can be cleaned up using household cleaners or a diluted bleach solution. There are certain precautions, though, that you’ll want to take.19
First, you want to make sure you’re wearing proper protection. This includes:
Essentially, you want to make sure your contact with the mold itself is as limited as it can be. When you’re cleaning it up, you’re going to be disturbing the mold itself, which will in turn release spores into the air. That’s why it’s important to protect your skin and eyes, and prevent yourself from breathing it in.
Pro Tip: Never, ever mix cleaning products. Some mixtures, like ammonia and bleach, can create toxic fumes that are way worse for your health than a little bit of mold on the shower grout.
Next, ensure the area you’re cleaning is as ventilated as possible, without spreading mold to other areas of your house. If you’re cleaning out moldy boxes from the basement, for example, open the doors to the outside, but close the door that leads upstairs.
Now, it’s time to remove the mold. You can scrub mold off hard surfaces with a brush and cleaner, but for more porous surfaces, like drywall, you’ll need to take precautions to not damage the material itself. If the mold is too embedded, you might have to remove and replace the material it’s been growing on.
Once you’re done cleaning, make sure you dry the area out completely. A fan can help speed this process along. You’re also going to want to make sure the mold doesn’t come back, so make sure you’ve identified and taken care of the source of the moisture that allowed it to grow in the first place.
Pro Tip: If you’re having problems with recurring mold, the room you’re cleaning might be too humid. Invest in a dehumidifier to remove ambient moisture from the air pesky mold is relying on.
To summarize the process of mold removal, follow these steps:
The above steps should really only be taken if a mold problem is relatively minor. For mold contamination larger than 10 square feet, the EPA recommends calling in a professional.20
If your mold problem is widespread, it might be too much for you to safely handle on your own. That’s when a professional mold remediation specialist can become a lifesaver. But what exactly do they do, and what will it cost? We have more in our guide to mold remediation, but here’s a quick overview.
If you know you have a mold problem, it’s probably a waste of time to have an inspection or to call for a mold test. We explain everything in our mold test breakdown, but all an inspector will do is confirm the presence of the mold, and all a test will do is tell you what kind of mold it is. If the problem is big enough that you’ve noticed it, and you know you can’t handle it on your own, it’s time for remediation.
Pro Tip: It’s good advice to avoid companies that will both test for and remediate mold. They always have a vested interest in “finding” a problem.
Here’s what will likely happen, depending on where the contamination is located and the extent of the problem:21
Depending on the services offered by the mold remediation professional, they might also fix broken or leaky plumbing and repair or replace the materials they needed to remove. If not, they should at least give you a framework for how to make sure the mold won’t return. Make sure you speak with the remediation specialist to understand exactly what the scope of work involves.
Generally speaking, mold remediation costs anywhere from $13 to $30 per square foot.22 Depending on the extent of the problem, it can take anywhere from a couple of days to a couple of weeks to get your home mold-free.
Pro Tip: Don’t think if you have a major mold problem that you can rely on your homeowners insurance. We have more in our guide to mold insurance, but the long and short of it is traditional policies won’t cover mold remediation. For that, you’ll need to purchase additional coverage.
Now let’s turn our attention to the best and worst states for mold.
You might expect that the worst states for mold are the ones with the most tropical climates, like Florida. That’s not really the case. According to American Risk Management Resources, climate is not the main determining factor in mold risk. According to their most recent study, they are:23
And the best five are:
These findings disprove the notion that more humid climates are the worst ones for mold. As it turns out, it has way more to do with building practices than your specific region. This is why it’s important for each and every family to stay vigilant in protecting themselves, whether you live in Las Vegas or Tallahassee.
We hope this guide has been informative and answered all of your questions. We think the key takeaways are these:
So that about does it for this comprehensive guide to household mold. Stay safe out there, and remember, you won’t regret buying a dehumidifier!
In most people, limited exposure to mold will not cause serious illness. It could, however, trigger allergic responses that include coughing, sneezing, and sore throats.
If you suspect your home has mold, getting a professional test won’t hurt. However, if you can see or smell a large contamination, it’s best to skip directly to professional remediation.
Each situation is unique, but the EPA recommends calling in professionals if your mold contamination has spread beyond 10 square feet. Large-scale contaminants can be dangerous if not handled properly.
Cleaning small mold contamination usually isn’t too difficult, but if the mold has penetrated the surface — if it’s growing on ceiling tiles, for instance — you might need to remove and replace the contaminated material.
A bleach diluted with water will take care of most surface molds, but commercial products are available specifically designed for mold cleanup. Never mix cleaners, though. You could create toxic fumes.
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With a decade of experience as a journalist, Derek Prall has been covering cybersecurity for seven years. He has spent more than 1,000 hours researching digital privacy and has covered almost 100 topics related to VPN and identity theft protection. Previously, Derek has covered tech issues at American City & County magazine, where he won numerous national awards for his cybersecurity coverage. His areas of expertise included network security, big data analytics, and AI applications in public safety. Derek graduated with dual bachelor’s degrees in English and Communications from Furman University and now lives in Atlanta, Georgia, with his wife and two cats.