How to Interpret Mold Test Results and Mycotoxin Findings
A plain-language guide to understanding mold test results, mycotoxins, and why air, dust, and surface tests often produce different findings
Who This Guide Is For and When It Applies
This guide is written for homeowners, Indoor Environmental Professionals, clinicians, and remediation specialists who are trying to understand why different mold and mycotoxin tests can produce confusing or seemingly contradictory mold test results.
It explains how air, dust, and surface measurements relate to different environmental questions, and why those measurements should not be treated as interchangeable.
This guide does not define health thresholds, medical diagnoses, regulatory standards, or remediation requirements. It explains how to interpret results within the physical and scientific limits of what each type of test can show.
What This Guide Is Based On: Research From Part A
This guide is grounded in Part A of our scientific preprint series, which examines why mold test results and mycotoxin measurements often produce different or seemingly conflicting findings. By breaking down these differences, this post equips you to approach mold test results with confidence, avoiding common pitfalls in interpretation.
Rather than evaluating which test is “better,” Part A explains why disagreement occurs in the first place. Mold and mycotoxin tests measure different indicators, in different environmental domains, and over different time scales. As a result, divergence between results is expected and does not necessarily indicate testing error or analytical failure.
For readers who want the full technical and scientific explanation, you can review the complete Part A research here: View the Part A scientific preprint
The Most Important Question to Ask About Mold Test Results
Before looking at any mold test results, ask:
What question was this test designed to answer?
Some tests are designed to show where mold is present in a building.
Others are designed to show whether airborne mycotoxins may be present in the air people are breathing.
When a test is used to answer a question it was not designed for, confusion and misinterpretation follow. This principle is key to making sense of mold test results, whether they’re from air sampling or dust analysis.
Two Different Concerns: Mold and Mycotoxins
Many people use the phrase “toxic mold” as if it describes one thing. In practice, it usually combines two very different concerns.
Mold Spores in Air and Mold Growth (Biological Questions)
These questions focus on the mold itself. This includes mold spores in the air and mold growth on materials, which help show where mold is present and how it may be spreading.
Mold-focused testing is commonly used to answer questions such as:
- What mold species are present in this space
- Are mold spore levels in the air typical or elevated compared to outdoor or reference conditions
- Is there evidence of hidden growth inside walls, ceilings, or building materials
- Is this mold commonly associated with water damage or indoor moisture problems
These questions are about source identification and building conditions, not chemical exposure.
Airborne Mycotoxins and Chemical Exposure Questions
These questions focus on toxins made by some molds, not the mold itself.
Mycotoxins are non-living chemical substances that can attach to very small airborne particles or remain as residue in dust and on surfaces, functioning as particle-associated chemical contaminants rather than living biological agents (Bennett and Klich, Clinical Microbiology Reviews, 2003).
Mycotoxin-focused testing is commonly used to answer questions such as:
- Are airborne mycotoxins present within the breathing zone during sampling
- Are those mycotoxins associated with fine or ultrafine particles that may persist in suspension
- Is there residual mycotoxin contamination in dust or on surfaces after cleaning or remediation
These questions are about potential chemical presence and residue, not about identifying where mold is growing.
What This Means for Your Mold Test Results
Mold testing helps show what mold is present and where it may be coming from.
Mycotoxin testing helps show whether mold toxins are present in the air, dust, or on surfaces.
One focuses on the source. The other focuses on possible environmental presence or residue.
The Three Measurement Domains in Dust vs Air Mold Testing
Environmental testing does not just measure “mold” or “toxins.” It measures different parts of the indoor environment.
In Part A, the scientific preprint underlying this guide, three analytical domains are defined. Each represents a different physical view of what is happening indoors.
The Airborne Domain (Indoor Air Quality and Mold Spores)
This domain represents what is suspended in the air within the breathing zone during the time of sampling.
Air testing is commonly used to:
- Identify mold spores in air and mold species
- Compare indoor and outdoor spore levels
- Evaluate whether airborne mycotoxins may be present in inhalable particle fractions
This domain answers questions about what people may be breathing at that moment in time.
Airborne measurements represent time-resolved conditions within a defined sampling window, not a cumulative or historical record of building conditions. These measurements are governed by fine and ultrafine particle behavior, airflow patterns, and ventilation dynamics rather than long-term surface accumulation (Morawska and Nazaroff, Indoor Air, 2013; Nazaroff, Indoor Air, 2014).
The Dust Reservoir Domain (Historical Mold and Mycotoxin Presence)
This domain represents material that has settled and accumulated over time on floors, shelves, and other surfaces.
Dust reflects weeks, months, or even years of environmental history, depending on cleaning habits, airflow, and building use.
Dust testing is commonly used to:
- Identify mold species associated with long-term presence or water damage
- Evaluate historical contamination patterns
- Assess whether mycotoxins are present as chemical residue
This domain answers questions about what has been in the building over extended periods, not what is currently in the air.
Dust-based indicators are most appropriately interpreted as time-integrated surface reservoirs rather than as proxies for conditions relevant to inhalation exposure at the time of sampling (Nazaroff, Indoor Air, 2014).
The Surface Domain (Surface Mold Testing and Localized Residue)
This domain represents what is present on a specific material or location.
Surface testing is commonly used to:
- Confirm visible or suspected mold growth
- Verify cleaning or remediation effectiveness
- Check for localized mycotoxin residue
This domain answers questions about a specific area, not the whole building or the breathing zone.
Why Mold Test Results and Mycotoxin Results Diverge
It is common for air, dust, and surface tests to produce different answers. This does not mean a test failed.
It means different physical processes are being observed.
Particle Size and Why Dust and Air Behave Differently
Dust is dominated by larger, heavier particles that settle out of the air.
Mycotoxins, by contrast, tend to associate with fine and ultrafine particles that are much smaller and can remain suspended in the air for long periods. Fine and ultrafine particles dominate indoor air by number rather than by mass and exhibit extended suspension times and enhanced transport into occupied breathing zones (Morawska et al., Atmospheric Environment, 1999; Hinds, Aerosol Technology, 1999).
Because of this:
- Dust often reflects historical biological material and chemical residue
- Air often reflects what is currently suspended in the breathing zone
This helps explain why airborne mycotoxins may be detected in air when little appears in dust, or why dust may show contamination even when air appears clean.
Current understanding of how specific mycotoxin classes distribute across indoor particle size ranges is informed primarily by aerosol physics and surface chemistry models rather than comprehensive field characterization. These relationships should be interpreted as conceptual and exposure-aligned rather than as precise quantitative partitioning (Morawska and Nazaroff, Indoor Air, 2013).
Common Misunderstandings About Mold Exposure and Mycotoxins
“If a mold species can make mycotoxins, then toxins must be in the air”
Not necessarily.
Some molds can produce mycotoxins, but that does not automatically mean those toxins are present, airborne, or associated with inhalation-relevant particles at the time of testing. Mycotoxin production and environmental persistence depend on growth conditions, substrate chemistry, and physicochemical transport processes rather than on spore presence alone (Bennett and Klich, Clinical Microbiology Reviews, 2003).
“If it is in the dust, it must be in the air”
Not necessarily.
Dust represents what has settled over time. Air represents what is suspended right now.
Material can exist in one domain without being present in the other because surface reservoirs function as long-term sinks rather than dynamic representations of breathing-zone aerosol conditions (Nazaroff, Indoor Air, 2014).
Professional Interpretation and Domain Boundaries
This section is intended for Indoor Environmental Professionals, consultants, and technically engaged readers who need to apply Part A’s framework in formal reporting, real estate, insurance, or remediation contexts.
It does not introduce new methods or standards. It clarifies what the framework allows and does not allow you to claim.
Understanding Uncertainty and Variability
Environmental measurements reflect a dynamic system, not a fixed condition.
Factors that can influence results include:
- Time of day and occupancy, where movement resuspends particles
- Ventilation and pressure differences, such as open windows or HVAC cycling
- Cleaning activity, including vacuuming or wiping that alters dust and surface results
- Weather and humidity, which affect particle suspension and settling
Because of this, any single result should be treated as a snapshot within a changing environment. Episodic fluctuations in airborne chemical presence can occur without new source activity due to resuspension and humidity-driven interfacial partitioning (Morawska and Nazaroff, Indoor Air, 2013; Ferro et al., Aerosol Science and Technology, 2004).
What Each Domain Allows and Does Not Allow You to Claim
The Airborne Domain Boundary
Airborne results describe conditions within a defined sampling window and breathing zone. They do not describe:
- What has been present historically in the building
- What is embedded inside materials or hidden cavities
- What may appear under different occupancy or ventilation conditions
Air results should be framed as time-specific environmental indicators, not permanent building conditions.
The Dust Reservoir Domain Boundary
Dust results describe what has accumulated and persisted over extended time periods. They do not describe:
- What occupants are breathing at a specific moment
- How particles are distributed vertically or across rooms
- Whether contaminants are currently being resuspended
Dust should be framed as historical and contextual evidence, not as a proxy for real-time exposure.
The Surface Domain Boundary
Surface results describe one location and one material at a time. They do not describe:
- Whole-building conditions
- Airborne distribution
- Exposure magnitude
Surface testing should be framed as localized confirmation and verification, not as a general environmental assessment.
Using Multiple Domains as Context, Not Confirmation
Cross-domain comparison can strengthen interpretation, but only when used as a consistency check, not as proof.
Examples include:
- Dust shows contamination, but air does not, suggesting historical presence without current airborne relevance
- Air and surface both show residue, suggesting localized persistence or resuspension
- Air shows spores, but dust is clean, suggesting recent disturbance or short-term source
Agreement across domains strengthens contextual understanding. Disagreement highlights differences in time scale, particle behavior, or sampling focus rather than analytical failure.
Reporting Clarity for IEPs and Consultants
Best practice within this framework includes:
- Labeling mold test results by domain, not just by test type
- Separating mold findings from mycotoxin findings in reports
- Stating the time scale each result represents
- Explicitly noting when a result is being used for context rather than exposure or source determination
This reduces the risk of cross-domain misinterpretation by clients, clinicians, or third parties.
Relationship to the Scientific Framework
This guide is a plain-language interpretation of the Part A scientific preprint, which establishes the physicochemical basis for divergence among mold spores, dust indicators, and airborne mycotoxin measurements in indoor environments.
The preprint formalizes:
- Analytical domain non-equivalence across air, dust, and surface measurements
- Biological versus chemical hazard class distinction between mold and mycotoxins
- Particle-size–dependent behavior governing suspension, settling, and persistence
- Temporal mismatch constraints between time-resolved air samples and time-integrated reservoirs
- Limits on cross-domain inference and the role of consistency checks rather than substitution
For formal definitions, figures, and scientific references, consult the Part A Scientific Preprint.
Final Takeaway
Clear interpretation of mold test results begins with a clear question.
If you are trying to understand where mold is growing, focus on tests that reveal biological presence and building conditions.
If you are trying to understand what people may be breathing, focus on tests that measure airborne chemical and particle behavior.
Different mold test results answer different questions. Using them together correctly leads to clarity instead of confusion.
You Do Not Have to Figure This Out Alone
If you are unsure how to interpret your mold test results or decide which type of test makes sense for your situation, a short conversation can help. We offer a 15-minute consult to help homeowners and professionals clarify next steps. This discussion is informational only and does not provide medical, legal, or regulatory advice.
References and Scientific Basis
This guide is based on the Part A scientific preprint and established literature in aerosol physics, indoor air quality, and mycotoxin research. Outbound links are provided for transparency and academic verification.
- Ritacco, M. (2026). Physicochemical Divergence of Biological and Chemical Indicators Across Airborne, Dust, and Surface Analytical Domains in Indoor Environments. Respirare Labs Preprint Archive. Internal Preprint Link
- Morawska, L., and Nazaroff, W. W. (2013). The evolution of indoor particle research. Indoor Air, 23(6), 442–454.
- Nazaroff, W. W. (2004). Indoor particle dynamics. Indoor Air, 14(Suppl 7), 175–183. https://pubmed.ncbi.nlm.nih.gov/15330785/
- Hinds, W. C. (1999). Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles. Wiley.
- Bennett, J. W., and Klich, M. (2003). Mycotoxins. Clinical Microbiology Reviews, 16(3), 497–516. https://pmc.ncbi.nlm.nih.gov/articles/PMC164220/
- Ferro, A. R., Kopperud, R. J., and Hildemann, L. M. (2004). Source strengths for indoor human activities that resuspend particulate matter. Environmental Science and Technology, 38(6), 1759–1764. https://pubmed.ncbi.nlm.nih.gov/15074686/
- Morawska, L., He, C., Hitchins, J., Mengersen, K., and Gilbert, D. (1999). Characteristics of particle number and mass concentrations in residential houses. Atmospheric Environment, 33(23), 3891–3899.
About this Guide
This guide interprets Respirare Labs’ 2026 Part A preprint on physicochemical divergence across airborne, dust, and surface mycotoxin measurement domains.