How to Test for Mold in Your Home

If you suspect that mold spores are polluting your indoor air quality or making you sick, testing your environment should be at the top of your to-do list. Here’s how to get an accurate reading on a mold testing kit.

By Deirdre Mundorf and Glenda Taylor and Bob Vila | Updated May 11, 2022 3:57 PM

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Have you ever walked into a bathroom and wrinkled your nose because the space was so musty? It’s not news that damp quarters are prime breeding grounds for mold and mildew, fungi that help natural elements break down so that they can biodegrade. But while their presence might be vital to your compost pile, it’s unwelcome in homes and buildings. When fungi spores  become airborne and are inhaled, your health can suffer.

Sometimes, a mustiness is accompanied by other clues of the presence of mold: discolored spots on walls and floors, development of respiratory problems, and noticeable humidity. Other times, it’s less obvious that there’s a problem at all. If you’re concerned that the air in your home is compromised by mold, you can find some peace of mind knowing exactly how to test for mold.

RELATED: The Dark, Dirty Truth About Household Mold (and How to Get Rid of It Yourself)

Lucky for you, testing is as simple as purchasing a viable mold test kit and collecting samples in strategic locations following the instructions outlined below. After testing, one of two things will happen: The results will come back negative, which signals that the musty smell is a temporary, easily remedied issue. Or, your test reveals the presence of mold in your home. If your test results are positive for mold spores, the best course of action is to send the test to a lab to determine what type of mold it is and how to effectively treat it.

Before You Begin

Mold requires moisture to grow, which is why you’re most likely to find it in damp, humid areas. Plumbing leaks, for example, often trigger mold growth and should be repaired as soon as you find them. Visible mold anywhere in the home should be removed promptly by following safe mold removal methods, or by hiring a professional mold removal company.

What about that mold growth that you can’t see? If you notice a musty smell but no visible signs of mold (black, white, or brownish coating), you may have mold growing where you can’t see it. The following are some of the most common spots for mold to grow undetected and are thus smart locations to test for mold:

RELATED: 14 Things You Absolutely Must Get Rid of If Your Home Floods

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The Most Common Types of Household Mold

While there are thousands of species of mold in existence, most homeowners are concerned about Stachybotrys chartarum, commonly known as “toxic mold” or “black mold.” This species of mold is actually quite rare, but it’s one of a number of molds that produces a high level of mycotoxins (dangerous mold-based chemicals) that can create a hazardous home environment. That said, any species of mold can become a health risk if it’s allowed to grow out of control. To be on the safe side, all mold growth identified by a viable mold test should be treated and removed quickly.

Below are some of the more common types of mold that can be found in a home.

  • Mucormycetes: Mucormycetes fungi, including Cunninghamella bertholletiae, Rhizomucor species, and Syncephalastrum species, are most commonly found in the soil during the summer and fall. It is difficult to avoid these molds completely, but they are generally harmless to most individuals.
  • Alternaria: Alternaria alternata is an allergy-causing mold that is prevalent in the environment and may be brought into a home from the outdoors. Once inside, it can spread quickly through the home, so prompt removal using a cleanser with bleach is important.
  • Aspergillus: While most prevalent in the air, Aspergillus can also be found in soil, compost piles, stored grains, and decaying plants. Once brought inside a home, it can grow and spread over surfaces such as clothing, leather, or building materials, particularly in moist areas.

How to Use a Mold Test Kit

Mold test kits are widely available from home improvement stores and from online retailers, but not all test kits are the same. Some are designed to only determine whether mold is present on surfaces. To test for mold spores in the air you’re breathing, you’ll need to purchase a viable mold detection kit such as Seeml Labs’ Mold Inspector in a Box. Most quality mold tests cost between $20 and $45.

The entire testing process will take a few days. If the test you perform determines that mold spores are present in your home, you can then send the testing materials to a lab that will perform another test to determine what type of mold is present. This lab analysis can run an additional $40 to $70.

Note: The U.S. Environmental Protection Agency does not endorse any brand of home mold test kit. Rather, it recommends that homeowners have their homes professionally tested if they are concerned about the presence of mold. So, use these do-it-yourself kits with a grain of salt: They can be helpful in confirming suspicions if you’re on the fence about whether you have a mold problem. Of course, if the symptoms are visible and dire, it’s best to call in the pros to test for mold and remove colonies from your home.

STEP 1: Close off the space.

Close the windows and doors in the room you’ll be testing 24 hours before performing the test. This allows potential mold spores to congregate without being disturbed by drafts.

STEP 2: Set up the test kit.

Remove the contents of the kit from its packaging. Typically, you’ll find at least a shallow plastic or glass petri dish with a lid and a label. The inside of the petri dish has been treated with a substance known as a “microbial culture” that promotes the growth of mold spores. This should help you collect an adequate sample when testing for mold in the amount of time recommended by the manufacturer.

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STEP 3: Leave the petri dish alone for a few days.

Remove the lid from the petri dish and place the dish (open end upward) on a flat surface at about table height.

Leave the petri dish untouched for about 48 hours. This time may vary slightly depending on the manufacturer’s instructions. During this time, restrict traffic in the room during the test period if possible to keep from disturbing the air. Cover the doorway with a strip of painter’s tape, if you need to, as a reminder to household members and guests that this area is temporarily off limits.

STEP 4: Seal the petri dish and stow it in a dark space.

Place the lid back on the petri dish after the waiting time has passed, and put a layer of tape around the seam where the lid meets the dish. Either scotch tape or electric tape works well, but avoid using a tape that’s difficult to remove, such as duct tape. 

Write today’s date on the label enclosed in the kit and affix the label to the bottom of the petri dish. Place the taped petri dish in a dark location, such as a dresser drawer or on a closet shelf.

STEP 7: Observe whether mold appears in the dish.

Check the petri dish in two days for signs of mold growth within the dish. If mold is present, it will look similar to the mold you’d find growing on old food in the fridge.

  • If the petri dish shows no signs of mold, return it to the dark spot and check it again daily. If your test for mold turns up nothing after a total of 5 days (from the date on the label), you can throw the dish in the trash—the kit did not find mold in the room.
  • If mold is present in the dish, you can send the petri dish to the lab recommended by the manufacturer to determine the type of mold you have and the course of treatment. Many kits include an envelope for mailing. You’ll also have to send payment for the analysis.
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STEP 8: Consider additional tests as you wait for professional results.

Allow 3 to 8 weeks to receive your results. Meanwhile, you may wish to continue testing for mold throughout the house. While a variable mold test can tell you if mold spores are present in a specific room, you’ll need to use additional kits if you want to test other rooms in your house.

Health Dangers from Prolonged Mold Exposure 

Anyone can suffer from breathing air contaminated by mold spores. The risk of health problems increases for those with known allergies, compromised immune systems, and respiratory disorders such as asthma. Mold-related symptoms include:

  • Chronic coughing or wheezing
  • Shortness of breath
  • Frequent sneezing
  • Irritated or itchy skin
  • Watery eyes
  • Running nose
  • Chronic headaches
  • Skin rashes
  • Chronic fatigue
  • Memory loss and diminished ability to concentrate (associated with toxic mold)

Final Thoughts

With the wide range of potential health problems associated with mold, it is important to take steps to detect mold in your home quickly and remove it promptly. Follow the steps outlined above for how to test for mold to help you and others in the home breath more easily. You can also consider investing in an air quality monitor to provide additional reassurance that the air in your home is free of mold and other harmful pollutants.

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FAQs About Mold Testing

Due to the complexities and importance of learning how to test for mold, it is understandable if you have a few remaining questions. Consult the FAQs below to learn more about mold inspection and testing.

Q. What’s the difference between mold and mildew?

While you may hear the terms mold and mildew used interchangeably, there are some key differences between these two organisms. While mildew is always flat or powdery in appearance with a white or gray color, mold is often raised, fuzzy, or slimy and can be different colors such as black, green, blue, or red.

Another key difference is that mold can burrow beneath the surface, while mildew is a surface fungi that is easier to spot. Mold also poses greater health risks than mildew. In addition to causing respiratory problems, like mildew, it can also have a negative impact on the nervous system.

Q. What does black mold look like?

Black mold looks like a black stain. It is most often found in areas of higher moisture, particularly in those that have been flooded. Another key detail for black mold detection is that it often follows a circular growth pattern. Look for round patches growing together; some may be smaller than an inch, with others being much larger.

Q. What does mildew look like?

Mildew is typically gray or white in color. It is a surface mold that stays flat as it grows. Mildew can also have a powdery consistency.

Q. Can a person be tested for mold exposure?

While there are some tests designed to identify mold exposure, they are not 100-percent reliable. However, your primary care physician may be able to assess your symptoms and perform blood tests or skin-prick tests to learn more about your sensitivity to mold.

Q. Will mold test kits detect mold growing inside of walls?

Removing mold on the walls is important, but you also need to know how to detect mold in walls to ensure that the issue is fully remedied. Mold test kits detect mold in the air. So, if the mold spores inside the wall are getting into the air, they will be detected. Otherwise, the test kit may not find mold growing inside the walls.

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