Alternaria mold spores and hyphae from an indoor surface (C) Daniel FriedmanReasons to Test for Toxic or Allergenic Mold
Guide to Good Practices in Mold "Testing"

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Why is mold testing sometimes useful and appropriate? Here we list reasons to test for the presence of mold or to collect samples to identify the kind of mold present in buildings.

Why try to identify mold at all. Some practitioners argue that no mold testing is ever needed, mold should simply be found and cleaned-up.

We agree with this approach for small areas of mold where there are no larger issues such as occupant complaints or BRE (building related illness).

And we warn that there has developed an entire industry of folks who perform comparatively useless and sometimes expensive "mold tests" in or on buildings.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

When is it Useful to Test for & Identify Mold in Buildings?

Very moldy building interior (C) Daniel Friedman15th Annual North Carolina/South Carolina
Environmental Information Association Technical Conference
Myrtle Beach, SC
Daniel Friedman 23 September 2005
updated thorough 11/19/2013

[Click to enlarge any image]

Only an idiot, or perhaps someone out to prey on mold fear (MYCOPHOBIA, STAINS MISTAKEN for MOLD) would require a mold test to determine if the home at left needs professional mold remediation.

But there may be valid reasons to identify the dominant mold contaminants in a building.

In this article series we discuss the validity of nearly all of the popular mold testing methods currently in use, pointing out the strengths and weakness of each approach to mold sampling in the indoor environment, beginning with air sampling for airborne mold levels indoors.

The appropriateness of testing at all is discussed on this and other pages at our website.

Mold testing discussion can be divided into two main topics, the first of which is discussed in this paper.

  1. MOLD TEST REASONS - reasons why in some conditions it is appropriate, useful, and cost-justified to test for mold and to identify the kinds of mold that are present in a building.
  2. MOLD TEST vs. PROBLEM DIAGNOSIS - what is the difference between "mold testing" and "mold identification", and what good are consumer mold test kits. Why are "mold tests" alone of little use and insufficiently diagnostic?

While mold "testing" is in our opinion far too often abused and while it is too easy to waste money on tests that are either unreliable or insufficiently diagnostic, nevertheless there are at least these reasons that call for indoor mold testing, provided it is properly conducted.

  1.  SAVE MONEY if it's Just Cosmetic Mold - avoid unnecessarily costly cleanups of harmless mold or stains
  2.  MOLD RELATED ILLNESS- information to aid the physician
  3.  MOLD CLEANUP DATA BASELINE- manage large, costly mold remediation projects and prove cross-contamination
  4. LEGAL PROCEEDINGS may include a requirement for technical documentation that a building is mold-contaminated.

Why identify mold - Reason 1: Cosmetic-only vs. problematic mold

Small areas of mold, no complaints or other concerns? Just remove it and fix the cause. We emphasize that for small areas of mold contamination, generally where less than 30 square feet of contiguous mold is present, simple building cleaning and renovation procedures are all that's needed and testing is usually not appropriate. Most building mold contamination falls in this first category.

Watch out: it is not necessary to identify the mold genera/species to write a mold remediation plan. The mold genera/species will not normally affect the dust containment nor mold cleanup or remediation procedure. However we have on occasion found large ane very expensive mold remediation projects whose sole target was a reservoir of compeltely harmless "black mold" that in fact was not growing in the building, that came in on framing lumber, and that has no impact on the lumber nor on the building and its occupants - other than being ugly.

Even larger areas of mold may be harmless and do not require costly cleaning methods. If mold present in the building is only of "cosmetic" concern, it is unlikely that special cleanup methods such as negative air, establishment of a containment system, and special personal protection for workers is needed. If these special methods can be avoided, the cost to remove mold will be substantially less.

Therefore it cases where a large amount of mold is present it may be appropriate to have an expert perform testing and to prepare an appropriate remediation plan to guide the remediation contractor. The same expert may be used to perform clearance testing later to assure that the cleanup was proper and successful.

Also see Can mold make you sick?"

Harmless Cosmetic "Black Mold": A very common example is the Ceratocystis/Ophistoma group which appear as "black mold" on framing lumber and which are more commonly known as "blue stain" or sapstain molds. This mold is found on lumber as it arrives from the lumber yard - a condition that is readily apparent to a building expert and which can be confirmed by sample identification.


Allergenic mold: Other dark molds, including the most common genera Cladosporium sp. are often allergenic: a potential respiratory irritant or a problem for people with allergies, asthma, or other sensitivities.

Toxic/Pathogenic mold: a third broad group are molds which we call "toxic" and includes species which are toxic, pathogens, or infectious agents which in some cases may be capable of infecting humans or of producing disease in humans. Aspergillus flavus, A. niger, are two examples.

We find in many cases that large areas of "black mold," about which owners/occupants may be unduly frightened, are Ceratocystis/Ophistoma, a common mold that is found on framing lumber from time of construction, and which is known to be only of cosmetic concern, and which is not an indicator of mold-conducive conditions in the building - it came in on the lumber and is inactive and cosmetic.

Without knowing what this is, people may make large and inappropriate expenditure on "professional remediation" - in one case in CT a client was about to launch a $600,000. complete re-framing of the first floor of a building, a totally inappropriate step which was completely unnecessary with a little knowledge of mycology and building science.

Ambiguous airborne mold counts: A second example of this sort is the need to distinguish between two "mold counts" that appear to be the same but actually mean very different things. An outdoor 500 Pen/Asp spores/M3 of air and an apparently low indoor 400 Pen/Asp spores/M3 may take on a new meaning if the outdoor spores are a different genera/species than the indoor ones.

Watch out: air tests and culture tests for mold are at high risk of false negative results.


And while mold counts or scores are very helpful in interpreting mold test results, the lab report accuracy is quite vulnerable to mistakes in sample collection. Numbers in technical reports often give a false sense of accuracy.


Why identify mold - Reason 2: convey possible health effects to a physician

Proving that mold in a building caused a health concern is so arduous and costly as to be inappropriate in most cases. If a lot of allergenic or toxic mold is present, it needs to be removed. But information about what was found in a building may be useful: a number of our clients have health complaints for which IAQ problems are a potential cause or contributor - information which they want to convey to their physician.

For example, a delay in diagnosing fungal infections in two of our clients led each to have permanent loss of eyesight. We acknowledge that these cases are not common, but they occur enough for caution to be in order. We don't submit that we should be practicing medicine nor diagnosing ailments, rather that information about a sick person's environment might be useful to their physician.

Dr. Harriet Burge (ret) at the Harvard School of Public Health has taught me that the cost of proving that a specific illness is caused by a specific mold or allergen in a particular environment is so arduous as to be impractical. However we agree, as we expect you do too, that if a large area of allergenic or more toxic mold is present in an environment it should be removed.

Can Mold Make You Sick?

We live in a sea of mold, and other stuff in the air we breathe, on cushions we sit on, clothes we wear, pools we swim-in, and so on. Most mold is not hurting anyone, and some of it makes us well when we're sick(Penicillium notatum, for example). Fear of mold (mycophobia) is unjustified and in our opinion, more a result of media hype, enviroscare, and gouging consumers.

A healthy person walking through a room of moldy air is not likely to die. On the other hand, there is a wealth of less rigorous empirical data matching occupant complaints with indoor mold and allergens.

Finally, for certain people, mold can be a serious problem if it's at high levels indoors.

It's an overstatement by those authorities who assert that "... there are no proven links between mold and illness." we refer readers to some of our lab's references for descriptions of illness-related molds, some of which are found in buildings:

  1. Ashley, Kevin, Ph.D. and Paula Fey O’Connor, NIOSH, NIOSH MANUAL of ANALYTICAL METHODS (NMAM), 5th Edition, (March 2017) NIOSH, DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Institute for Occupational Safety and Health, retrieved 2018/05/17, original source:
  2. Burge, Harriet A., William R. Solomon, and Michael L. Muilenberg. "Evaluation of indoor plantings as allergen exposure sources." Journal of Allergy and Clinical Immunology 70, no. 2 (1982): 101-108.
  3. Eduard, Wijnand. "Fungal spores: a critical review of the toxicological and epidemiological evidence as a basis for occupational exposure limit setting." Critical reviews in toxicology 39, no. 10 (2009): 799-864.
  4. Identifying Filamentous Fungi, A Clinical Laboratory Handbook, Guy St-Germain, Richard Summerbell, Star Publishing, 1996, ISBN 0-89863-177-7 (English)
  5. Fundamentals of Diagnostic Mycology, Fran Fisher, Norma B. Cook, W.B. Saunders Co. 1998, ISBN 0-7216-5006-6
  6. Atlas of Clinical Fungi, 2nd Ed., GS deHoog, J Guarro, J Gene, & MJ Figueras, Centraalbureau voor Schimmelcultures, Universitat Rovira I Virgili, 2000, ISBN 90-70351-43-9 (you can buy this book at Amazon) - The Atlas of Clinical Fungi is also available on CD ROM
  7. contains a more extensive reference list of mold investigation, mold lab procedures, and health references.
  8. Reponen, Tiina, James Lockey, David I. Bernstein, Stephen J. Vesper, Linda Levin, Gurjit K. Khurana Hershey, Shu Zheng et al. "Infant origins of childhood asthma associated with specific molds." Journal of Allergy and Clinical Immunology 130, no. 3 (2012): 639-644.
  9. U.S. CDC, BASIC FACTS [ABOUT MOLD] [PDF], Centers for Disease Control and Prevention,
    retrieved 2018/05/17, original source:

    Generally, it is not necessary to identify the species of mold growing in a residence, and CDC does not recommend routine sampling for molds.

Why Identify mold - Reason 3: establish a data baseline and later, evaluate the success of a professional mold remediation project

Where large areas of mold remediation are needed, using professional cleaning services, we find that in many cases the "professional" does not properly maintain containment, and actually increases the level of allergens in the building. In buildings where occupants are at particular risk (elderly, immune-impaired, infant, asthmatic) we have had cases where an occupant entered an area contaminated with high levels of allergenic mold and suffer severe asthma attacks. In Ellenville, NY at a private residence we learned of a fatality involving just such an incident.

For large remediation projects we find it very useful to have a base-line of data on what areas need to be cleaned and which are acceptably clean before the remediation project. Then a quick test after the remediation can confirm not only that it was successful, but that the remediator did not inadvertently fail to contain.

If the containment was unsuccessful and other building areas have become contaminated enough to want to have additional cleaning (typically HEPA vacuuming or wiping), having the baseline showing that the contamination followed the remediation rather than preceded it protects the property owner or occupant from additional unnecessary expense.

The usefulness of samples depends on the knowledge and thoroughness of the person collecting the sample as part of a building investigation. Arbitrary or random samples are unlikely to be a reliable characterization of a building. Choice of method as well as how the method is applied (for example, just where to stick the tape to collect a surface sample) makes a large difference in the quality and representativeness of the sample.

See MOLD / ENVIRONMENTAL EXPERT, HIRE ? for a discussion of when it is or is not appropriate, justified, and ethical to hire a mold consultant to inspect, diagnose, and advise about mold contamination in a building.

At DO IT YOURSELF MOLD CLEANUP we provide suggestions for a do-it-yourself cleanup of small areas of mold.

Mold Test Reason No. 4: legal proceedings, demands by attorneys or judges

In legal proceedings such as a TENANT LANDLORD MOLD DISPUTE the attorneys or the court may include a requirement for technical documentation that a building is mold-contaminated. While a suitable environmental expert could document and testify that there was actionable mold contamination based on a visual inspection, attorneys and judges may still insist on technical or lab tests as well.

Watch out: the typical and popular "quick and dirty" mold test approaches used by some investigators consist only of collecting air or culture or swab samples from inside the building. There is a significant risk of false-negative results of such tests - that is of failing to detect an important mold contamination problem that was not readily visible. See ACCURACY OF VARIOUS MOLD TEST METHODS

Watch out: a second error in demanding quantitative mold test results such as counts or scores is that no matter how precise the environmental test laboratory's report may be, the lab findings are no better than the intelligence that went into the actual sample collection in the field. Improperly collected air tests or culture tests and even surface sampling tests all are vulnerable to false results (missing a problem or reporting mold genera A as important when it is not and when mold genera B is actually far more of a hazard). See ACCURACY vs PRECISION of MEASUREMENTS

What these mold test reservations mean is that testing alone, without an expert inspection and history taking are at extra risk of false negative results: concluding that there is no mold hazard when in fact there is one. Like bird-watching, if we fail to look for birds where the birds are located, we won't see many of them.

OPM: Other People's Money

Unfortunately too often consultants recommend costly inspections and tests in order to reduce their own personal risk (that a client may later bring action for failure to recommend more aggressive measures) when the costs of those tests is borne by the client.

In my OPINION and experience, a busy attorney or judge may not feel able to afford the time to become technically informed about indoor environmental hazards such as mold contamination. It seems easier to simply require testimony or documentation by an expert even though a lay person, with a modicum of understanding, can certainly recognize whether or not there is a large area of indoor mold growth.

Details of how a visual inspection can identify mold are at MOLD APPEARANCE - WHAT MOLD LOOKS LIKE.

Watch out: a visual inspection alone, focused only on recognizing visible mold may fail to detect evidence of an important but hidden mold reservoir in a building. Omitting the recognition that building leak history (construction methods, materials, stains) and building maintenance can themselves be used to identify high-risk areas where further, more invasive inspection methods may be justified.

Absence of evidence is not evidence of absence.


Continue reading at MOLD CLEANUP GUIDE- HOW TO GET RID OF MOLD or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.



Or see MOLD / ENVIRONMENTAL EXPERT, HIRE ? where we discuss how to decide when building or occupant conditions appear to warrant hiring an expert.

Or see MOLD TEST vs. PROBLEM DIAGNOSIS where we explain the limitations of mold testing.

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MOLD TEST REASONS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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