A Guide to Interpreting Mold Test Results

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Guide to interpreting mold test results

Indoor mold is incredibly common. In fact, mold can be found in about 70% of homes in the United States. Although many molds are harmless, some types can pose serious health risks – especially in large quantities. 

That’s why it’s important to get your home professionally tested for mold if you suspect you have an issue. Professional mold testing will identify the type of mold in your home, the level of infestation, and the next steps to take.

Inspectors will usually take samples from different areas inside and outside your home and send them to a laboratory for testing. Then, they will provide you with a report that includes the test results.

These mold test results can be confusing to interpret, but understanding them is crucial for mold remediation. This guide will help you understand when to test your home for mold and how to interpret your mold test results. 

When Should You Test Your House for Mold?

Mold inspection and testing

Before diving into how to interpret mold test results, it’s important to know when you should test your house for mold in the first place. There are a few key times when testing is recommended. These include when you:

  • See visible mold growth
  • Smell musty odors
  • Know about or suspect water damage
  • Have suffered recent flooding or leaks
  • Experience sudden health problems (headaches, coughing, sneezing, watery eyes)

If any of these scenarios apply to you, it’s time to get your home tested for mold. In addition, if you are planning on selling your home, potential buyers may also request a mold test as part of their due diligence.

Types of Mold Tests

There are many different types of mold tests, and the one you choose will depend on your specific situation. Some of the most common include: 

Air sampling

Air testing equipment

Air samples are taken using a spore trap and sent to a lab for analysis. This test can tell you what types of molds are present in your home and the concentration of mold spores in the air.

Surface sampling

Mold surface sampling test

Surface samples are taken by swabbing or taking a piece of the affected area and sending it to a lab for analysis. This can identify the type of mold present but not the concentration.

Bulk sampling

Bulk sampling

Bulk sampling involves taking a sample of the affected material and sending it to a lab for analysis. This is often used when there is visible mold growth and can help identify the type of mold present.

What Can You Expect from a Professional Mold Test?

Professional mold inspection and testing

A professional mold test usually begins with an inspector looking for signs of mold, such as water stains, musty odors, or visible mold growth. They will also check for conditions that could lead to mold growth, such as water leaks or high humidity levels.

After the inspection, the inspector will take mold samples from different areas of the home or building. Typically, they will take surface samples and air samples – from both inside and outside your home. These samples will then be sent to a laboratory for analysis.

Once the mold test results are received, the inspector will provide a report that includes the type or types of mold present and the concentration of mold spores in the air. The report will also include recommendations for addressing the problem.

Reading and understanding mold test results can be challenging. Here, we will provide some guidance on interpreting these lab results.

How to Read Your Mold Test Results

Sample mold report

Interpretation of mold test results can be challenging, and many professional mold testers do not provide extensive information on what the information means. Unless you’re already an expert in mold testing and remediation, interpreting lab results requires some research.

There a several key pieces of information you’ll want to look for in your results. Once you understand these, you’ll better assess the severity of your mold problem and develop a remediation plan. The information you’ll want to look for includes:

The Type (or Types) of Mold Present

First, you’ll want to identify the types of mold present. Some types of molds are more harmful than others. As a result, knowing what you’re dealing with will help you develop an appropriate plan for removal.

Your mold test will likely state the mold present by its scientific name. Here are some of the most relevant molds your test results might identify, along with a brief description of each:


Penicillium and Aspergillus are two of the most common types of mold species found in homes and have over a thousand different species. These molds will grow with only the humidity in the air as a source of moisture – even in relatively clean environments. As a result, it is often difficult to completely eliminate these molds from your home, where many times the mold species outside the home are different than the ones inside the home.

However, large concentrations of either Penicillium or Aspergillus can cause health problems since these molds are allergenic. Allergic reactions to these molds can include watery eyes, a runny nose, coughing, and skin rashes. Additionally, immuno-compromised individuals may be subject to lung or sinus infections when exposed to large concentrations of these molds. Some of which are found in water-damaged buildings.


Cladosporium is another allergenic mold that can be found both indoors and outdoors. It will often grow on painted surfaces, wood, and fiberglass. Cladosporium is dark green or black in color and has a velvety appearance. 

Exposure to Cladosporium can cause allergic reactions similar to those caused by Penicillium and Aspergillus. Additionally, this mold has also been linked to asthma in some people.


Chaetomium is a type of mold that is often found in water-damaged buildings. It usually grows from wet insulation, drywall, and carpets. This mold type feeds and spreads quickly. Once it takes hold of a home, it can cause significant structural damage.

Like many molds, Chaetomium can cause allergic reactions. Additionally, this mold has been linked to skin infections in some people and is a producer of mycotoxins.


Basidiospores are produced by mushrooms and other fungi. They are often found in damp, shady areas outdoors, such as wooded areas or near bodies of water. However, basidiospores can also be found indoors, growing on wet surfaces or humidifiers.

These molds are not as allergenic as others on this list. However, they can still cause respiratory problems in some people and structural damage to buildings. 

Stachybotrys (Black Mold)

Stachybotrys is a genus of mold that includes the type often referred to as “black mold.” It is found in water-damaged buildings and usually grows on wet cellulose materials, such as insulation, drywall, paper, and cardboard. Stachybotrys spreads quickly and can cause structural damage to a home.

This mold is particularly dangerous because it produces toxins called mycotoxins. These toxins can cause various health problems, including respiratory infections, rashes, headaches, nausea, and fatigue. In addition, exposure to Stachybotrys can lead to serious neurological problems and even death in severe cases.


Memnoniella is a type of mold that is closely related to Stachybotrys. The two species are often found growing together. Like Stachybotrys, Memnoniella grows on water-damaged cellulose materials and produces mycotoxins.

If your test results identify any of these molds, you will likely need to take action to remediate the problem. Otherwise, toxic molds can spread further and cause adverse health effects and structural damage.

The Concentration of Mold Spores

In addition to identifying the types of mold present, your test results will also give you an idea of the concentration of mold spores in the air. The results will likely be given in spores per cubic meter of air (sp/m3). 

Generally speaking, a concentration of mold spores below 500 sp/m3 is considered normal. A concentration of mold spores above 500 sp/m3 is considered high. Therefore, if your report comes up with high concentrations of mold, it will likely advise you to remediate the problem.

However, it is important to note that even low concentrations of mold spores can cause health problems in some people. For example, if you or someone in your home has allergies or asthma, you should take action to remediate a mold problem even at low concentrations.

Note: your report will also include a “raw count” column. This is the number of each type of mold spore that was counted in the sample provided to the lab. Although important for lab purposes, the concentration (spores/m3) is a more accurate measure of the problem.

The Indoor/Outdoor Comparison

Your report will also compare the mold spore concentration inside your home to that outdoors. 

A high indoor/outdoor ratio indicates a problem with mold inside your home. If the indoor/outdoor ratio is significantly higher, the mold is likely coming from a specific source inside your home.

When the indoor/outdoor ratio is lower, it could mean that the mold spores are coming from outside and finding their way into your home. In this case, you will need to take steps to seal any cracks or openings in your home’s exterior. Your report will likely include specific recommendations for doing this. 

The Location of Mold Samples

To accurately assess the mold problem in your home, you will need to take multiple samples from different locations. The report should list the locations of each sample (e.g., “bathroom,” “bedroom,” ” attic.”)

This is important because it will help you identify the source of the problem. For example, if all samples with high mold concentrations come from the basement, the problem is likely originating there.

Recommendations for Further Action

Once you have received your test results, you will need to take action to remediate the problem. The report should include specific recommendations for further action, such as removing moldy materials or cleaning affected surfaces.

If the problem is widespread, you may need to hire a professional mold remediation company. In severe cases, you may need to move out of your home while the problem is being remediated. 

Whatever the case, it’s important to follow the recommendations in your report to ensure that the problem is properly remedied. Otherwise, the molds can spread further and cause adverse health effects and structural damage.

In Conclusion

Mold testing is important for assessing the health and safety of your home. By understanding your test results – you can take the necessary steps to remediate a mold problem if needed. This, in turn, will help to protect your family from the adverse effects of mold exposure and your home from further damage.

Need to Schedule Professional Mold Testing in New Jersey?

If you think your home may have a mold problem, the team at GreenWorks is here to help. We offer comprehensive mold testing and inspection services in New Jersey.

Our team of certified mold inspectors will come to your home, assess the problem, and take samples for testing. We will then provide you with a detailed report of our findings and recommendations for further action.

To learn more or to schedule service, contact us today or call us at (732) 223-2073. We look forward to helping you ensure a healthy and safe home for your family.

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Victor Coppola

Victor Coppola is a Building Biologist with decades of diverse environmental experience spanning natural resource management and contaminated sites to Indoor Air Quality (IAQ) and building hygiene matters. He focuses on the three most prevalent issues degrading today's built environment: Moisture Odor & Mold (M.O.M.). Mr. Coppola and his Team are sought out by individuals and professionals concerned about IAQ to those actually suffering from Biotoxin Illness. His hybrid blend of environmental interests and services enable him to give a unique perspective into today's changing environment. Think your home is killing you, better call Victor and his Team at GreenWorks.

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