Guide to Moldy Musty Smells in Buildings
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A guide to the probable sources of moldy or musty odors in buildings
Why do we smell a variety of different odors indoors, maybe from mold or from other sources?
How to identify odors or gases by type, source, and toxicity. Noxious odors or smells in buildings can be diagnosed and cured
Environmental safety advice for home owners & home buyers
Un-biased mold and mold odor removal advice from a neutral party
Questions & answers about finding & removing mold odors in buildings, furnishings, clothing, other items.

Mold & Musty Smells Explained: this web article summarizes the common sources and causes of moldy and musty odors in buildings. Here we explain the causes & cures of moldy smells & odors in buildings. We discuss how to track down a moldy smell to its source, possible health hazards where there are mold smells & MVOCs in buildings, and we describe how to clean out or remove moldy odors from buildings, furnishings, clothing, etc. This website provides articles on to diagnose, test, identify, and cure moldy musty odors in buildings.

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Readers should also see MVOCs & MOLDY MUSTY ODORS and see MYCOTOXIN EFFECTS of MOLD EXPOSURE. Also see How to Find & Remove Odors, Gases, & Smells in Buildings - our article covering all building odors and smells.

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How to Recognize, Identify, & Remove Moldy Musty Odors in Buildings

Mold Smell Basics - What You Need to Know

If you smell mold or "mildew" there's probably mold in the building. Most people correctly identify moldy or musty smells as "mold". Some folks call these odors "mildew-odor" but since mildew grows only on living plants, it's more accurate to call these indoor odors and growths "mold".
Not all mold makes moldy smells. So problem mold may be present but not smelly. Don't rely on odors alone to decide whether or not there is a mold problem in a building.
Mold smells are not necessarily dangerous but they indicate a problem. There have been suggestions that mold VOC's may be harmful and certainly some of our clients have that opinion. We 're waiting to read scientific studies which answer this MVOC question. Since if there is a mold odor there is will be one or more mold colonies in a building, we don't know if medical or other occupant complaints are really due to the odor or due to exposure to mold spores, allergens, or toxins.
If there's mold in the building it should be found, removed, and its cause corrected.
Costly mold inspection/testing may not be appropriate. See MOLD EXPERT, WHEN TO HIRE
Removing problem mold may not remove all moldy odors. Mold "odors" are probably MVOCs (Mold Volatile Organic Compounds) but these gases can permeate other soft goods like carpets, clothing, curtains, upholstered furniture and can be difficult to remove, though thorough cleaning and exposure to sunlight and fresh air will usually remove the worst of these odors.

Single individual mold genera/species may produce different moldy musty odors

There are some mold genera/species that produce a variety of odors (MVOC’s) depending on varying conditions of moisture and also what the molds are growing on, as well as producing odors only under certain conditions (particularly with variations in temperature and humidity, and perhaps light).

Our photo (left) illustrates that the source of a mold smell in a building may be hidden from view - in this case there was extensive mold found growing on the back (hidden side) of kitchen cabinets. The cabinet shown was removed to show the problem.

Different mold genera species may produce different moldy musty odors

There are building conditions that produce a variety of growing mold species - in a moldy building it is very likely that there are multiple species growing on various mold-friendly materials. Some mold colonies can be hard to spot. Certainly different species of mold respond differently to temperature, moisture, and nutrients they find. For example, one mold species is referred to as the "moldy gym socks" mold since it produces that odor.

Buildings with a moldy smell may have other odors or hazards not related to mold

Most people have a pretty good idea of moldy or musty smell as associated with mold. If you smell mold or find it at important levels in screening samples of air, dust, or vacuumed surfaces, (by quantity or by particle type in samples) it is probably there.

But it would be no surprise to find a variety of odors in a building coming from mold problems or from other problems there.

There can be lots of other odor sources in a building, including potentially dangerous ones such as heating appliance flue gases (which might include very dangerous but odorless carbon monoxide along with smelly combustion products) in a building. Other possible concerns that might produce strange smells include chemicals such as pesticides that may have been improperly applied. To identify other building mold odors see Odors, Smells, Gases in Buildings-Diagnosis & Cure.

Since lots of building conditions can cause odors (ranging from dead animals to sewer backups) and since some of them can be tough to track down (sun-heated plastic windows, window screens, or vinyl siding), also take a look at the links along the left of this page.

Variations in Conditions at a Building Cause Wide Variation in Mold Odors

Humidity changes cause mold to behave differently - species dependent, including release or not of spores, and release or not of MVOC's which is what you 're probably smelling. I've seen a very moldy college library go from almost no airborne mold to very high airborne mold when the humidity in the moldy basement was suddenly and significantly lowered. The change in humidity alone appeared to cause the mold (Aspergillus sp.) to begin releasing spores in visible green dusty clouds.
Wind of course might pressurize some building walls differently, causing wall cavity contents to be noticed or not. We've had reports of moldy odors coming from electrical outlets in windy weather; we postulated that wind may have been pressurizing the building's walls, causing moldy odors to leak into the living area from wall cavities where there was a pre-existing mold colony either on building material surfaces (wood, drywall) or in the wall cavity insulation.
Weather changes: such as a rainy season can produce changes in mold behavior and odors.
Temperature changes can cause mold to behave differently, in MVOC production, sporulation, or other growth stages.
Light & Other changes might also affect mold growth and behavior, such as changes in the level of light exposure or perhaps even seasonal changes.
Mechanical disturbance such as the agitation of moldy materials during demolition or cleaning can cause an extreme increase in the level of airborne spores and other fungal materials, and might increase the level of moldy odors as well.
Use of equipment, such as ozone generators, can produce other odors, not mold, but potentially indicating harmful or even dangerous conditions. See our Ozone Warnings article.

One cannot tell from smell alone whether the mold is a large or small area, nor can one tell by smell alone if the mold we smell is allergenic or toxic.

What to do about moldy odors in buildings

Knowing something about the history of the building and its prior occupants and uses can help point to directions of investigation. This is especially useful since there are no simple economical “catch-all” tests for chemicals or gases that cover every possible hazard.

Find the problem mold source

Follow your nose, use your eyes, but also think: where has there been a building moisture problem, roof leak, plumbing leak, sewer backup, or other moisture source. Investigate these areas by visual inspection. Mold tests can be useful but are no substitute for a careful visual inspection and history-taking if you want to find odor problems in a building. Our website provides in-depth guidance on what to do about mold. See in particular

Individual odor sensitivity varies widely

It is certainly true that individuals’ sensitivities to odors varies quite widely. Often one person in a building or family notices odors more than everyone else, just as sometimes only one family member is bothered or made ill by mold or allergens or other building contaminants.

For example some pregnant women experience an acute increase in odor sensitivity. I’ve conducted field experiments that demonstrated a remarkably accurate ability of a pregnant woman (who complained of odors in the home) to correctly identify materials emitting a particular odor even when others in the home didn't’t notice a thing.

Illness or even medicines can cause variations in odor perception

It’s also true that some illnesses can cause perception or misperception of odors (imagining smells) while other illnesses can interfere with one’s ability to sense an odor. So a thorough approach to odor complaints would include consulting with a physician. This is particularly appropriate if there were not an obvious in-building source, when only one person in a building perceives a problematic odor, or when someone already knows that they have an illness or complaint that may be odor-sensitive, such as Multiple Chemical Sensitivity or when someone is under particular medical treatments that may cause odor sensitivity problems to manifest themselves.

Return to Mold/IAQ Action Guide: What to do about mold, mildew, and other indoor allergens an environmental testing guidance website explaining what to do about mold, mildew, and other indoor allergens or go to More Information on Building Inspection, Testing, Diagnosis, and Repair Alternatives

Frequently Asked Questions (FAQs) About Mold Odor Troubleshooting in Buildings, Furnishings, Clothing

Question: black mold in my garage wall left a musty smell in clothing - will the smell go away ?

I have black mold in one wall of my garage, due to a leak. It is now being repaired. It smelled musty for about a year and I finally am getting around to fixing it. I use my garage as a closet for some clothing. I notice that the ones that have been there for a long time smell musty.

Do I need to throw them all away, or will the smell and any danger from the mold in the air that got onto the clothing simply go away in time? Many of these are clothes are vintage and have been in there for 10-20 years. I am not going to wash them- it's either they will be fine in time or I will sadly throw them away. There are too many to wash, iron etc. and some are too delicate or ornate to wash. Thanks, R.P.

Our photo (left) illustrates a leather jacket covered in heavy white mold growth. This item was beyond economical restoration.

Reply: clean clothing to get rid of mold odors; you may have to toss out carpets & some upholtered furnishings

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem that you haven't discussed such as making sure the mold cause is repaired and making sure you don't focus just on "black mold" missing other more toxic or harmful molds that can be present where wet conditions occur in a building.

That said, here are some things to consider:

The mold smell will dissipate but it is unlikely to go away, certainly not quickly and possibly never in clothing that remains enclosed, boxed, or in closets in a moldy or recently moldy smelly area. This is so even if there is no visible mold on the clothing, as fabrics absorb MVOCs - volatile organic compounds produced by many mold species under the right conditions.

Occasionally we can successfully deodorize a fabric or even a carpet by leaving it outdoors in sunlight for enough hours, but in my experience moldy-smelling clothes can best and most reliably be deodorized by being laundered or dry-cleaned successfully to remove mold and odors. On occasion I've had to run clothes twice through a washer. Or have them cleaned professionally.

If there is clothing that would be less costly to buy new than to have professionally cleaned, the choice is apparent: replace those items.

In contrast, moldy smelling upholstered furniture or carpets can be difficult or impossible to clean successfully and are usually tossed out.

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MOLD ODORS, Musty Smells in Buildings - see detailed links at page left

Building Odor Diagnosis & Cure References

Here are more references for diagnosing moldy, musty, or other building odors

How to Find & Remove Odors, Gases, & Smells in Buildings - our article covering all building odors and smells. Since there are many possible sources and causes of odors in buildings, readers concerned about mold or musty smells should also review the odor sources in this list.
Mold Odor FAQ's: If we smell mold, is mold present and is that a problem? Most people have a pretty good idea of moldy or musty smell as associated with mold. If you smell mold or find it at important levels in screening samples of air, dust, or vacuumed surfaces, (by quantity or by particle type in samples) it is probably there.
Mold Odors: Why do mold odors occur in our home following rain? Odors at exterior outlets sure sound as if there has been leakage into the wall and a probable mold colony. We need an expert visual inspection and possibly invasive sampling, combined with building history, to find and follow leak paths and high humidity cavities in order to inspect the most-likely mold reservoir targets in a building. The odors may be MVOC's which may be produced by some mold genera/species at varying levels as humidity, temperature, air pressure, and other variables change.
Mold Information Website: This website provides information and procedures for finding, testing, cleaning and preventing indoor mold, toxic black mold, green mold, testing building indoor air quality, and other sick house / sick building investigations. Here are research articles, inspection and testing procedures, and contact information for expert services. We give in-depth information about indoor air quality problems: causes of respiratory illness, asthma, or other symptoms such as neurological or psychological problems, air quality investigation methods, and remediation procedures such as mold cleanup, handling toxic mold contamination, and building or mechanical system repairs. We offer advice on mold prevention and mold-resistant construction resistant to indoor problem molds such as the Aspergillus sp., Penicillium sp. and Stachybotrys chartarum groups.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Environmental Health & Investigation Bibliography - our technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
Adkins and Adkins Dictionary of Roman Religion discusses Robigus, the Roman god of crop protection and the legendary progenitor of wheat rust fungus.
Kansas State University, department of plant pathology, extension plant pathology web page on wheat rust fungus: see http://www.oznet.ksu.edu/path-ext/factSheets/Wheat/Wheat%20Leaf%20Rust.asp
"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
US EPA - Mold Remediation in Schools and Commercial Building [Copy on file at /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
US EPA - Una Breva Guia a Moho - Hongo [Copy on file as /sickhouse/EPA_Moho_Guia_sp.pdf - en Espanol

Mold Contamination Testing, Cleanup, Prevention: references & products

The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems
Aerobiology, Building Science, Microscopy, & Laboratory References, an extensive technical bibliography
Allergens: what they look like in buildings
Associations: Sick House, Sick Building, SBS - Air Quality, Government, Private Associations and Information Resources
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
Atlas of Mold Related Illness: Index of Symptoms and health, physical, neurological, psychological, and other complaint which people suspect may be mold or building-related.
Atlas of Indoor Mold, Online Clinical Mold Atlas, Toxins, Pathogens, Allergens and Other Indoor Particles - Medical Health Effects of Mold (separate online document)
Black Mold that is Harmless Photos of recognizable, usually harmless black mold on wood, bluestain, ceratocystis, ophistoma
Building Floods: quick steps after a building flood or plumbing leak can prevent costly mold contamination
Classes of Mold: what types of cosmetic, allergenic, or toxic mold are a problem? Can mold be cleaned-up successfully?
Clinical Mold References - Detailed bibliography of mold reference texts
"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
"Disease Prevention Program for Certain Vegetable Crops," David B. Langston, Jr., Extension Plant Pathologist - Vegetables, University of Georgia (PDF document) original source: www.reeis.usda.gov/web/crisprojectpages/209797.html
"Disease Prevention in Home Vegetable Gardens," Patricia Donald, Department of Plant Microbiology and Pathology, Lewis Jett
Department of Horticulture, University of Missouri Extension - extension.missouri.edu/publications/DisplayPub.aspx?P=G6202
"Management of Powdery Mildew, Leveillula taurica, in Greenhouse Peppers," Ministry of Agriculture and Lands, British Columbia - Original source: www.agf.gov.bc.ca/cropprot/peppermildew.htm
Environmental Health & Investigation Bibliography - our own technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
Fiberglass: Mold in Fiberglass Insulation© 2005 comments about a field study in process, & more about health hazards from fiberglass insulation - DJF
Fifth Kingdom, Bryce Kendrick, ISBN13: 9781585100224, is available from the InspectAPedia online bookstore - we recommend the CD-ROM version of this book. This 3rd/edition is a compact but comprehensive encyclopedia of all things mycological. Every aspect of the fungi, from aflatoxin to zppspores, with an accessible blend of verve and wit. The 24 chapters are filled with up-to-date information of classification, yeast, lichens, spore dispersal, allergies, ecology, genetics, plant pathology, predatory fungi, biological control, mutualistic symbioses with animals and plants, fungi as food, food spoilage and mycotoxins.
Fungi, Identifying Filamentous, A Clinical Laboratory Handbook, Guy St-Germain, Richard Summerbell, Star Publishing, 1996, ISBN 0-89863-177-7 (English) (buy at Amazon)
Looking for Mold Procedure: what mold is often found where in buildings - simple technical presentation
Meruliporia: the house eating fungus or "poria"
Mold Action Guide: Step-by-Step Instructions, What to do about mold, mildew, and other indoor allergens
MOLD APPEARANCE - WHAT MOLD LOOKS LIKE Photos of what mold looks like in buildings
MOLD APPEARANCE - STUFF THAT IS NOT MOLD Photos of NOT-mold material that is sometimes mistaken for mold
MOLD ATLAS & PARTICLES INDEX, Pathogens, Allergens and Other Indoor Particles - Medical Health Effects of Mold (separate online document)
MOLD BY MICROSCOPE Mold under the microscope - photo identification of the most common indoor molds found in buildings
Mold FAQs Answers to Most Questions about Indoor Mold, Mold Related Illness, Mold Cleanup, Mold Prevention
US EPA: Mold Remediation in Schools and Commercial Building [Copy on file at /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
Mold spores in the Home - a Photo ID Library for detection and identification of mold allergens
Mold Test Kits - How to Collect and Send Your Own Mold Sample to our mold testing lab or to any mold lab you wish
Most Common Indoor Molds Found in Buildings, A Table of
Mycology, Fundamentals of Diagnostic, Fran Fisher, Norma B. Cook, W.B. Saunders Co. 1998, ISBN 0-7216-5006-6 (buy this book at Amazon)
Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
Rot concerns in buildings-some building mold such as Meruliporia incrassata "Poria" risks serious rot and hidden structural damage
US EPA: Una Breva Guia a Moho - Hongo [Copy on file as /sickhouse/EPA_Moho_Guia_sp.pdf - en Espanol

OTHER IAQ ISSUES: How To Find and Address Other Indoor Air or Indoor Environment Contaminants Besides Mold

Mold or allergens may not be the only or even the main indoor environmental contaminant. Don't let media attention to mold cause so much enviro-scare fear that other, possibly more urgent hazards go un-addressed.

Fiberglass building insulation and HVAC duct work insulation hazards
Sewage and Septic backup contamination in buildings: inspection, testing, remediation, & references to expert sources
Other environmental risks: Asbestos, carbon monoxide, electromagnetic fields, environmental illness, fiberglass, MCS - multiple chemical sensitivity, toxic gases, etc
Indoor Gas Sampling Plan for Residential Buildings lists a number of toxic indoor gases which we test for, depending on the building complaint and building conditions
Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
Pet control - if you can't say goodbye to your bird, cat, dog, guinea pig, hamster, tropical fish, then limit the areas they occupy and limit the airflow from that area to sleeping or other areas of the building, use allergenic bedding, eliminate wall-to-wall carpeting, improve housecleaning including use of a HEPA-rated vacuum cleaner. For more details see our article Dog, Cat, and Other Animal Dander - Information for Asthmatics and Indoor Air Quality
Rodents, Mice, Squirrel Control - I find high levels of mouse and rodent dander, fecal dust, and urine-contaminated dust in some buildings, and high levels of these materials in building insulation in those locations. If you have a mouse problem, particularly if mice and their waste (fecals or urine) are contaminating the building HVAC or building insulation, may need both steps to clean up or remove infected materials and steps to stop an ongoing rodent problem. If squirrels are a problem, the cleanup needs to include closing off entry openings into the building. Get some help from a licensed pest control expert.
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How to Recognize, Identify, & Remove Moldy Musty Odors in Buildings

Mold Smell Basics - What You Need to Know

Single individual mold genera/species may produce different moldy musty odors

Different mold genera species may produce different moldy musty odors

Buildings with a moldy smell may have other odors or hazards not related to mold

Variations in Conditions at a Building Cause Wide Variation in Mold Odors

What to do about moldy odors in buildings

Find the problem mold source

Individual odor sensitivity varies widely

Illness or even medicines can cause variations in odor perception

Frequently Asked Questions (FAQs) About Mold Odor Troubleshooting in Buildings, Furnishings, Clothing

Question: black mold in my garage wall left a musty smell in clothing - will the smell go away ?

Reply: clean clothing to get rid of mold odors; you may have to toss out carpets & some upholtered furnishings

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Building Odor Diagnosis & Cure References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Mold Contamination Testing, Cleanup, Prevention: references & products

OTHER IAQ ISSUES: How To Find and Address Other Indoor Air or Indoor Environment Contaminants Besides Mold