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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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
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.
Reader 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.
Reader Question: moldy odors in a home subjected to flooding: what should I do?
I live in a property which is situated on a flood-plain (the property does flood, last back in Feb 2011) and has no damp-proofing, so I've been told. The property has a strong damp odour, especially noticeable after a few days away from the place.
My clothes and other soft furnishings (and skin) really pick up the odour, and it's quite a stench that's makes me feel a little sick (it's really noticeable when visiting other peoples' homes and not so much living in the place as if I become more habituated to the odour) and it's just not a damp smell on clothing, bed linen etc, there's a kind of burnt wood/old wet wall plaster smell as well, quite hard to explain really but not nice.
So I was wondering if you had any idea what could be going and if the odour could be carrying mold toxins/VOCs and getting into my body and could be making me gradually sick over a prolonged time (I do get painful sinuses and joint aches and pains which blood tests show negative). Should I be getting some kind of biotoxin blood test done? And what tests should I be having done in the property? Any information and advice is welcome. - M.B. 12/20/2013
I forgot to ask about whether using fans to help control mold growth is a good idea. One of my bedroom walls collects condensation in cold weather (earlier in the year I found black mold under the wall paper so stripped the paper and painted that particular section of wall, you can now see water on the wall...haven't a clue what's going on under the rest of the paper in the room or actually in the walls it!) and in the conservatory, having no heating collects a load of moisture, with the problem of the wall areas growing black mold.
So I like to use fans in these places to help to evaporate moisture and to help keep dry-would this be helping to spread mold spores as a family member seems to think?
A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. You will find additional depth and detail in articles at our website. That said I offer these comments in reply to your email:
1. If you smell mold, there is almost certainly mold somewhere in the building, in quantity large enough to produce enough mold-volatile-organic-compounds (MVOCs) that you smell it. And indeed, some people can have an allergic, asthmatic, or other healt-related problem from MVOCs - that's well documented. It's also the case that chronic exposure or even a single or infrequent but very strong exposure to MVOCs can sensitize someone so that they suffer in the future even from lower MVOC exposure. That's been my experience as well as something corroborated by reading the literature.
From just your email no honest investigator could nor would attempt to diagnose the problem - but it sounds as if you need an expert on-site investigation to understand the building's leak history, what has been wet, where water or moisture are or have been present in the structure, where the highest risk areas are, and what mold contamination is found in those areas.
The result should be an action plan: what needs to be done to remove the problem (we remove it we don't "treat" or "kill" it), and what needs to be done to stop a recurrence.
The article MOLD / ENVIRONMENTAL EXPERT, HIRE ? - has advice on how to decide if it's justified to bring in an expert. Beware of amateurs who promise miracle cures - except for small do-it-yourself-scale mold cleanup projects, you're usually wasting your money and you may be risking making matters worse.
2. Using fans or other equipment to reduce indoor humdity can in general reduce the tendency of a building to grow problem mold indoors, but using fans also enormously increases the level of airborne dust. So I think the first order of business is to understand what's going on with the building and what needs to be done about it.
Continue reading at MVOCs & MOLDY MUSTY ODORS or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: terrible cat urine odor under new windows
(Aug 6, 2011) Marylyn said:
Hi and Help
I have a terrible smell of cat urine coming in under my new windows when it rains or when the wind blows.
I had all of the windows replaced last fall with high quality windows (older one were cheap builder windows), including installing a sill pan system, and we even opened under the windows during installation to check the wall cavities and they were dry and mold free. I also replaced all the insulation under the windows with new (I have even wet this new insulation to smell it and it is NOT the smell I smell). Now with the new windows, I have this terrible cat urine smell. It did not start till this spring and hasn't stopped. I had a mold expert come out and do wall moisture readings. They were fine.
I had air sampling done. It was negative. The window company is coming out to rip out the wallboard under the new windows to see what it is. Do you have any idea or experience with what we might find? I am bracing myself for bad news. Once many many years ago we had a cat urine smell in the basement and found some wet carpet. Once dried and cleaned, the smell was gone forever. This is much MUCH worse. I'm at my wits end over this. Thank you for such an informative site.
PS I wanted to add I am doing your spot odor testing (with the foil and tape and paper towel) to the inside wall as well as the outside window caulking--which has a similar cat pee smell but not as strong.
Reply: check for sun-heated plastic or vinyl building materials and other odor sources
Marylyn there are some things that can produce a pee smell besides cats, including other animals (mice, rats, in walls for example) and even some fungal growths. I would not do any costly demolition before being pretty sure where the smell originates. And I agree that air testing to try to track down odors is rather iffy.
Even if the test confirms something that's present, unless it's unique, like "heating oil fumes" you won't be any closer to the source. Use the smell test and people who have a good sense of smell along with our other odor track down instructions.
If you find that the odor is coming from new materials (windows?) it may be related to plastics or glues that will outgas - and it may be possible to speed that process up.
(Aug 6, 2011) Marylyn said:
The smell is most definitely coming in from under the windows. In fact, there is an outlet between two windows and it does not smell even when the smell is the strongest (as in the smell is not coming from the wall between them but actually under them). In a strong wind, the smell is ghastly. GHASTLY. As soon as the wind stops, so does the smell. We are at the point where we have to do something.
Fortunately the space between the window and the floor in this room is quite small (they are tall windows and sit about 10 inches off the floor). The area to be opened is narrow (about 6 inches from the bottom of the casing to the top of the floor molding). Out-gassing from a window installation should not stink like this for 6 months. It's an all brick home with no evidence of any animal entry. Thanks!
if you had water leaks at the windows there could be a mold contamination problem in the wall cavity and sometimes even in the floor cavity below those openings. It is worth taking a look.
Question: cat pee odor in commercial office building
(Sept 15, 2011) Ann said:
I manage a commercial office building of 15 floors and we have an issue with the "cat pee smell" on the west side of the building, which is the most exposed to the elements. It is only on 2 floors - the 5th on the north-west side and 8th on the south west side. We have tested for mold and none was detected.
This odor only occurs after a heavy rain that blows from the west. We have opened up at the corner columns but have limited space to investigate (about 4" wide) due to ventilation shaft. This building was built in 1967 and there has not been any major work done such as replacing windows etc..... for a number of years so we are at a loss. Any ideas on this ?
Ann, if you search our site for
A black light can help pinpoint the pee spots for cleaning and perhaps coating with a post-fire type odor sealant, and of course you need measures to encourage kitties to pee elsewhere. I use mothballs, bleach,or Fabuloso cleaner-soap as a deterrent, along with access restrictions.
See these urine odor detection & removal articles
Question: mold smells like wood
(Nov 30, 2011) Please help! said:
I don't find any info anywhere else, so I ask my question here:
Is there some mold that smells like wood? We have a lot wood (floor, roof, doors...) in here... Our apartment is 20 years old, so those should not smell so much anymore? The smell has been bothering me since we moved in. If I've been somewhere for a day or more, when I get back home I can clearly smell something weird "woody" smell in the air. I cannot find the actual source of the smell and my nose gets used to it in 5-10 minutes. We have sauna(a real sauna! :D) here, and smells a bit the same, but the bathroom door stays closed most of the day, so it cannot come from there... What can it be? Is not "musty" or "wet" smell.
Thank you for answering...
(Dec 13, 2011) Trudy Duffman said:
Just a comment. Ensure that you do not have Boxwood shrubs outside under the windows. Those bushes smell just like cat urine and especially if trimmed or when it rains or the wind blows.
Question: odors when it snows
(Dec 29, 2011) Jane said:
I have a question: I live in Southeast Michigan. This fall myself and several people I know have had strange allergic reactions. From hives to rashes, especially on the face, eyes and neck, or severe sinus issues with asthma like breathing difficulties. When it gets cold or snows it goes away, when we get warm temps 40 and above it comes back. I suspect allergic reaction mold but never had reactions like this.I also notice a smell of something like "burnt-dirt". Especially in wooded areas. When I smell this smell I usually start having reaction shortly after.
It is only outside. This smell I have also smelled in the past when passing an auto industrial plant. Could this be mold? What type might it be? I don't live near an auto plant but do have wooded like area behind my house. Recently I have been noticing it now coming when the heat comes on too. This is new and up till Dec. did not smell it in the house. Any help???
CHeck first for blocked plumbing vents
Question: moldy christmas decorations smell
(Dec 30, 2011) debbie said:
I have a new house and moved in 6 months ago. Christmas decorations smelled moldy when opening the plastic containers. Upon looking further I noticed white moldy looking spots on the concrete garage floor under the metal shelving where these containers are stored. These same containers were used in the old garage where I lived for 22 years and never had this smell. Do I have a problem?
Debbie, paper boxes and some similarly mold-friendly materials can of course support mold growth. The white spots on the garage floor may be effloresence, not mold - search InspectApedia for "effloresence" to see photos to identify that material. But since effloresence indicates moisture, that supports mold growth on other organic surfaces like paper or wood.
I can't say if you have a problem. But I'd clean up moldy stuff or throw it away, and I'd fix the water entry problem.
Question: terrible mildew odor
(June 21, 2012) Sue said:
I am renting a ranch home. I have been there 3 months, after the first month there was a terrible mildew odor in the air as well as from bathtub faucets. I called landlord, they poured some sort of bacterial cleaner down drain. The odor is much better, but every so often I smell it. I decided to perform a mold test and have it sent to a laboratory. These are the results, cladosoporium 12, rhoboturula 2, non-sporulating fungi 1, yeast 7. Do you think there would be any problems staying here until year lease over or recommend to move?
Sue, since true mildew only grows on living plants, what you smell, indoors, is certainly a moldy odor in the air. Your mold test is basically unreliable since it relies on mold cultures - only 10% of molds will grow on culture, so in using a mold test kit alone, without an inspection, to screen a building for mold contamination, you risk being 90% wrong the moment you opened the box.
No one who is informed, competent, and honest, would try to guess at whether or not your home is safe, much less if you should move, based on such incomplete evidence. Take a look at
Question: old people smell
(Sept 20, 2012) jamie said:
I have lived in my house for over 25 years. We noticed a smell right away, but my ex thought it was the smell of "old people and their belongings." We painted before we moved in, but, unfortunately, after moving in, we "lost" the smell. Others never wanted to hurt our feelings and didn't say anything. It wasn't until about 10 years ago, I realized that the smell was still there. I have been trying to figure the source out, but am losing the battle. The smell is still there. What can I do?
Jamie, try the odor diagnostic suggestions starting at ODOER GASES SMELLS DIAGNOSIS CURE
Question: how to find hidden mold
(Dec 27, 2012) John said:
I'm working for a lady who bought a wooden hutch from China. It has a musty smell. The owner is allergic to the smell, so she asked if there was anything I could do. She also asked if this would just be a coverup for the smell. I mixed 1/2 white wine vinegar and 1/2 water and misted the piece. I'm wondering if this will only mask the problem or should it take care of the problem. I was thinking it may have been a tongue oil that they put on the piece to ship it. Anything you can help me out with would be much appreciated. Thank You!
(Mar 11, 2014) SteveB said:
I work in an industrial building, in 2012 we, all the employees started to notice a smell like, mold or mildew. The management in charge has had many companies in to try to tract down what the odor could be through air quality tests and mold tests without any luck. The odor is so bad that after being in the building for 5 to 10 minutes your clothing smells like mold, leather belts, shoes, wallets, and cell phone cases seem to pick up he smell the worst.
I have gone to work for an hour then left to a doctors appointment, when I walk into the doctors office the others in the office can smell me as aoon as I walk in the door. Whats funny is the people and staff say "it smells like there is mold here".
Another issue is that you can smell the mold smell when you walk in the building at work, but after about 10 seconds of being in the enviroment you cannot smell it anymore, you have to be out of the building for about 30 to 60 minutes before you can smell it. The building we are in does leak water whenever it rains or there is a snow melt, but we have been told they cannot find mold. Many symptoms have shown, fatigue, hives, mood swings, upper respitory problems, problem with throat. Some people seem more sensitive then others.
Steve, if at the top of this article you click on "Click to Show or Hide Related Topics" you can find a link to our article titled
HIDDEN MOLD, HOW TO FIND
that should be helpful. Usually if you smell mold there is a mold reservoir somewhere; not all molds make notable odors but many do; so absence of odor is not proof of absence of mold; but the reverse, that if you smell mold there is mold, is usually reliable.
Air tests for mold, performed alone without a competent inspection and history taking are junk science.
Question: carpet smells like yeast
(Apr 27, 2014) Jan said:
I have a light patch on a carpet that smells like yeast. Can it be mould? How should I treat it?
Jan I don't think one can say what a yeasty-smelling light patch on carpet is from just that description. Sure it could be mold, or a spill, or food or something else.
Clean the stained area.
Question: leaky roof, mold smells
(July 11, 2014) Brandie said:
Ive been renting my house for about a yr now the landlord said she would fix the roof from leaking about 3mths ago she hasnt so when it rains my roof leaks real bad on the insulation ive been smell mold in my room for awhile (its on the top floor) there is black spots on the ceiling in my living room and the basement really smells bad like mold i have childern in the home and i suffer from a cough that just wont go away i not for sure what to do the landlord knows the roof leaks but wont fix it any suggetion
You might point out to the landlord that a leaky roof is
- likely to lead to more costly repairs from leak damage and mold
- failing to deliver a habitable rental space (probably violating your lease)
Question: house leaves moldy smell on clothes
9/26/2014 Cynthia Klein said:
My home leaves a musty smell on all my clothes. Really notice it when I am away from home traveling and open my suitcase . . . strong musty smell.
I have not found any signs of mold or mildew. I have inspected outside the home, inside the home, and underneath the house. The smell is persistent in all weather, wet and dry.
I do not know who to hire to come out. One company wanted me to spend $18,000 to install a barrier that sealed under the house. Having never seen water under the house and have inspected it during all seasons, I felt like they were trying to sell me their product without it being the cure.
Is there someone out there that just "inspects only" without a product they are trying to sell?
While indeed if there is a dirt crawl space below a home that can be a source of moisture and mold. Mold is not necessarily visually obvious, but is probably present if you smell mold. In any event certainly I would not pay thousands of dollars to "solve" what may be the wrong problem. First we need a reliable diagnosis of the problem.
Try the EXPERTS DIRECTORY at page top links, but also be sure to discuss your needs, concerns, and the experience of the inspector before hiring someone. Don't hire someone who just does an "air test" - what's needed is a careful interview, history of the building, and visual inspection, possibly supplemented by a test or two.
I agree that you should not hire an inspector who will also sell you the cure. Ask that question too.
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