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Mold protection gear being worn in this photo includes respiratory protection and a jumpsuit. Needed were eye protection and perhaps gloves.

Guide to Moldy Musty Smells in Buildings
EnviroAPedia ^©

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

Our site offers impartial, unbiased advice without conflicts of interest. We will block advertisements which we discover or readers inform us are associated with bad business practices, false-advertising, or junk science. Our contact info is at inspect-ny.com/appointment.htm.

This website provides articles on to diagnose, test, identify, and cure moldy musty odors in buildings. Mold & Musty Smells Explained: this web article summarizes the common sources and causes of moldy and musty odors in buildings. Also see How to Find & Remove Odors, Gases, & Smells in Buildings - our article covering all building odors and smells. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

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).

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.

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 my 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.

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

Use links just below at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

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CONTACT Daniel Friedman - Dan is a senior ASHI home inspector, nationally recognized expert on building inspection, building failures, and sick building investigation Contact Daniel Friedman for website content suggestions or for fee-paid consulting

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