How to Test for Mold in Your Home

If you suspect that mold spores are polluting your indoor air quality and aggravating allergies or making you sick, testing your environment is the best option. Here’s how to test for mold and get an accurate reading.

By Deirdre Mundorf and Glenda Taylor and Bob Vila and Evelyn Auer | Updated Mar 7, 2023 9:36 AM

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how to test for mold

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 its 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.

Lucky for you, testing is as simple as purchasing one of the best mold test kits and collecting samples in strategic locations following the instructions outlined below. After testing, one of two things will happen: The results could come back negative, which signals that the musty smell is a temporary, easily remedied issue. 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.

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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 produce 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. “All molds have the potential to cause reactions in those individuals who are susceptible to mold [such as those who have allergies or respiratory disorders],” says Karen Peissinger, industrial hygiene generalist at the University at Buffalo. “Also, that susceptibility can range from no reaction to a severe reaction, just like with dog and cat allergies. Thus, cleaning up any mold using proper methods is important.” 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. It is dark in color and has a velvety texture. 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.

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Where to Look for Signs of Mold in Your Home

In many cases, mold’s location can provide clues as to its cause. For example, mold on a window sill may be an indication that the window is not sealed properly, leading to leaks. The following are some of the most common spots for mold to grow undetected and are thus smart locations to test for mold:

  • Behind the refrigerator
  • Under stacks of newspapers or cardboard
  • Behind the drywall in wall stud spaces that contain plumbing lines
  • Under sinks
  • Behind the wallboard around leaking windows
  • In ventilation ducts
  • Under carpeting that was wet at one time (flooding, carpet cleaning)
  • On the back side of acoustic ceiling tiles (if roof leaked)
  • Behind any drywall that has been affected by a home flood
how to test for mold

How to Test for Mold Using a Test Kit

Home 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 $10 and $40. The entire testing process will take a few days. If the mold test comes back positive, you can then send the testing materials to a lab to determine what type of mold is present which can have an additional cost.

Note that the Environmental Protection Agency (EPA) does not endorse any brand of home mold test kit. Rather, it recommends that homeowners pay for professional mold inspection costs if they are concerned about the presence of mold. “If it is a large amount of mold, then the homeowner should contract with experienced assessment and remediation professionals. Ideally these professionals would hold valid credentials for mold assessment and mold remediation,” says Peissinger. “Also, some states have their own mold certification or licensing program. One more thing, to avoid conflict of interest, the mold assessor should be independent of the mold remediation company.” 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 right away. Search for “mold testing near me” to find a professional in your area who can detect and remove mold from the home.

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. If there is visible mold anywhere in the home, it won’t be necessary to test for mold before cleaning it or hiring one of the best mold removal companies. According to Peissinger, “Mold testing is not necessary in the vast majority of cases. If mold is visible, it should be cleaned up properly.” She recommends consulting EPA guidelines to find out how to remove mold safely.

What about mold growth that you can’t see? If you notice a musty smell but no visible signs of mold (a black, white, or brownish coating), you may have mold growing where you can’t see it. In this case, take the following steps to determine if household mold is present. Be sure to take the proper precautions to avoid inhaling or coming into contact with mold spores.

Tips for How to Get Rid of Mold

  • It is possible to kill mold with a few common household products such as vinegar or a mixture of baking soda and water.
  • For mold growth that exceeds 10 square feet, the EPA recommends professional cleanup. Professional mold remediation costs $2,242 on average.
  • After removal, the best way to prevent mold and mildew is to reduce the home’s humidity and eliminate any water leaks.

Safety Considerations

  • Anyone can suffer from the effects of exposure to mold spores, but the risk of health problems increases for those with known allergies, compromised immune systems, and respiratory disorders—even if the home has been allergy-proofed.
  • Some symptoms and signs of mold exposure can include coughing and 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.
  • When handling or cleaning mold, it’s a good idea to wear gloves, goggles, and a mask for protection.

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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.

how to test for mold

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 transparent tape or electrical 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 spot, such as a dresser drawer or on a closet shelf.

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STEP 5: Observe whether mold appears in the dish.

Check the petri dish in 2 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 detect 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, and you’ll also have to send payment for the analysis.
how to test for mold

STEP 6: 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. It may be worthwhile to look into who to call for a mold inspection if you suspect that the problem is extensive.

Since there is a 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 breathe more easily. You can also consider investing in one of the best air quality monitors to provide additional reassurance that the air in your home is free of mold and other harmful pollutants.


Because of the complexities and importance of learning how to accurately 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, mold 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 cleaned after flooding. One of the signs of black mold is a circular growth pattern. Look for round patches growing together; some may be smaller than an inch, with others being much larger. Use a black mold test or schedule an inspection to verify if black mold is present.

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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