Mold Smell: Don't Risk These Alarming Signs You May Have A Problem

I think you'll agree with me when I say: It's very startling to have a mold smell or mildew smell in the home…

Most of the time, home owners think they have a serious mold problem if they can't find the cause of the smell.

But Is it mold?

Just because you have a musty smell present in the house, it does not directly indicate a mold problem.

There are also a variety of other odors that can easily be confused with mold, however, if you do have an odor caused by mold, it was caused by one major thing:


Mold can't grow and thrive without it…

The smell of mold has an extremely distinct odor. If this is something you think you are dealing with, you will want to go through this entire article.

And if the smell is not mold, you will be able to properly diagnose it and get rid of the odor.

That's right, no more people covering their noses when they come into your home!

Is It A Mold Smell Or Mildew Smell?

Mold smell and mildew smell are generally used interchangeably when referring to "that" smell in the home.

But are they the same thing?

Yes and No.

Mold and mildew are both fungi.

While both from the same family there are many differences.


The main difference is mildew generally grows on surfaces whereas mold will actually penetrate the surfaces.

When the average person is referring to an moldy odor or mildew odor, they generally are referring to the same thing.

What Does Mold Smell Like

Mold has an odor that can be described as wet and musty. The foul odor can resemble the smell of decaying food or garbage.

Keep in mind that mold can often look different and smell a little different depending what type of mold and what type of surface it is growing on.

But think back to your high school locker room after gym class.

Remember that horrible combination of stinky socks, sweaty people and just overall yuckyness? That's another synonym for what mold can smell like.

Here are two easy ways to get a more exact idea of what mold smells like:

  1. Do a load of laundry. Instead of taking it out and putting it in the dryer, keep the clothes in the washer with the lid closed. Now leave it there for three to five days. Open that lid up and you will get an odor very similar to mold and it will not be pleasant!
  2. Leave a towel outside for a couple of weeks in the summer time. Go back and smell that towel and you will smell the odor of mold. ( You can also use a towel for about a week after you get out of the shower and it will start to get the same type of odor to a lesser extent)

Why Does Mold Cause A Pungent Odor

Mold growth itself does not smell bad. It is the off-gases that are let off by mold growth called Microbial Organic Compounds (MVOCs).

The dank musty odor signifies the presence of microbial volatile organic compounds (MVOCs). Traditional volatile organic compounds (VOCs) are mainly industrial made chemicals with low molecular weights, high vapor pressure and low water solubility. MVOCs are released from metabolic processes of decay agents like fungi, bacteria and biofilm. The off gassing of MVOCs include a wide range of alcohols, ketones, aldehyde, esters, carboxylic acids, lactones, terpenes, aromatic hydrocarbons, sulfur and nitrogen compounds.


You don't need to know scientifically how MVOC's are formed, however, you must know it is caused in most causes by water damaged porous materials. This could mean drywall, clothes, flooring, etc.

Bottom line is this:

If you have had a leak in your home that was not dried up properly or maybe a hidden leak that led to mold growth…


You have identified mold as the source of the moldy smell in your home.

Does Black Mold Smell Worse Than Regular Mold?

Black mold refers to a type of mold called Stachybotrys which is just one specie. Because takes a large or hidden chronic leak for black mold to grow for a long time, the odor of black mold is typically more potent than other mold spore types.

The odor that Stachybotrys lets off can also be much more harmful to your health as well because the off-gassing can let off toxins.

But don't be fooled, many other species of mold can cause an odor outside of black toxic mold.

Common Causes Of Water Damage Leading To Mold Smells

There are multiple reasons why your house can smell moldy due to mold but they all have one common factor which was stated earlier…

Water damage.

It can come in many forms:

  • Roof leaks
  • Plumbing Leaks
  • Window Leaks
  • Appliance leaks such as your refridgerator line or ice maker
  • Air conditioning leak
  • Etc.

When these types of leaks aren't cleaned up quickly, mold can start to grow and let off odors.

What Causes A Basement To Smell Like Mold

Basements tend to smell like mold because they are typically more damp which allows mold and mildew to grow and thrive. Being underground, a basement is not only susceptible to water intrusion at the foundation, but also warmer air entering the building envelope which leads to condensation.

If your like me and you grew up having an unfinished basement you probably have an odor that comes to mind…

Just that damp/mustiness odor.

This not mean that your basement is dirty. You can vacuum and mop all you want but if you do not resolve the root of the problem it will do you no good.

As stated above, basements tend to have more moisture. It's just the way it is.

It's important to find out if moisture is entering your basement in other ways, as well. If you notice a broken seal on a window or a crack in the foundation wall, you may have found your musty culprit. You should also check to see if you have clogged rain gutters, French drains, sewer backups, leaky pipes or even a broken seal on your laundry dryer vent as these problems can all contribute to a musty basement.


Problems In The Attic Leading To Musty Odors

Odors that are caused by issues in the attic can be a nuisance because they are not simple to diagnose.

The most issue to diagnose is of course roof leaks. You start seeing stains when it gets bad enough and you easily figure it out.

Unfortunately, it's not always quite that simple.

There are other issues that can arise in the attic that can lead to your home smelling like mold.

It could have been a problem brewing for years since the day your house was built or it could have been due to the things moved around by people that were doing work in the attic.

Improper Insulation

Improper insulation can lead to moisture problems in attics. This may not be a bigger problem in some areas of the world compared to others. In humid tropical climates, if an attic is not properly insulated, this can lead to hot and humid air to enter wall cavity space. The mixture of hot air within the wall cavity and cold air in the air conditioned ambient air space can lead to condensation.

Condensation can lead to mold growth…

Mold growth can lead to odor.

Got that?

I know that can be a bit confusing so let me show you exactly what I am referring it:

This photograph was taken in an attic.

Just imagine that piece of drywall extends down about five feet where there is a drop down ceiling. That entire wall cavity five feet isn't insulated.

All that hot/humid air (which on this day it was 128 Degrees) was going into the wall space between the drop down ceiling.

And this was the result….

Mold growth on the drop down ceiling below in a closet.

Improper Installation Of Ceiling and walls

Sometimes builders are unfortunately incompetent or are completely rushing through jobs and don't think about consequences of installation.

Vitutally, the same effect can happen as a not properly insulated areas. If drywall is not installed correctly hot air can enter the wall cavity space.

Here's an example:

The hot air in the wall cavity mixed with cold air in the living space created a dew point which led to condensation.

This particular house had a potent mold smell and sure enough, there was some mold within the wall space.

Leaky or Sweating Ducts

Central HVAC units have ductwork to distribute air (cold in the summer time) throughout the home.

When it gets more humid in the attic space during those summer months, and the colder air that is being distributed is the perfect recipe for condensation.

This is normal to a certain extent. There may be condensation dripping in the attic from time to time, but if your HVAC system is working properly, it shouldn't be excessive and you should have insulation in place to absorb the minor drops of water.

If there is excessive water dripping from the ducts….

You are in trouble!

You can see the ductwork is excessively sweating.

While the insulation can take some punishment, it's not waterproof.

Eventually, that ceiling it is covering will start to get wet and mold can start to grow.

Take a look at the back of the ceiling underneath this leaking ductwork:

Unfortunately, without infrared technology, there was no visual way to tell there was water damage, but you can sure as heck smell it!

For some reason or another, no staining appeared on the ceilings from the living space.

Why Does Mold Grow Behind Wallpaper?

Mold can grow behind wall paper due to the trapping over moisture. This is especially true in bathrooms where there is constantly a dew point created. The presence of a leak can accelerate mold growth behind wallpaper as well.

These problems can remain hidden for a long time because…

Who thinks to actually look behind there?

I mean, you have to start removing wall paper just to see what's going on.

That means if you ever had a leak in an area with wallpaper or humidity issues , the source of your mold smell may be mold trapped behind wall paper.

Taking moisture readings with a moisture meter may be a good first step. If your walls have been holding moisture for a long time, you may want to pull back the wall paper to further investigate.

Mold In The Air Conditioning System

Mold can grow on just about any porous material that is wet, but microbial growth can also form on one very important fixture in your home….

Your air conditioning system.

Keep in Mind:

If you have cental HVAC, an air conditioning system involves three separate components:

  • The compressor which is generally outside
  • The air handler which is generally indoors where usually the blower and coils are located
  • The Ductwork which is how the air is distributed throughout the home


Here is what you must know:

Mold generally won't grow on most building material that makes up your air conditioning system.

The reason why is because most items aren't porous.

That being said…

Mold can grow on the dust and dirt that is accumulated within the HVAC system.

Mold absolutely loves the dust, dirt and debris on the coils and within the duct work. Often times mold that is present within the coils can cause a strong potent odor that may be the source of the mold smell in your home.

It's not just the coils and ductwork that you need to worry about, the plenum boxes under the air handler are also. These boxes are sometimes fiberglass.

Here is an example of what may be under your central air handler:

In this particular case….

It looks EXACTLY how it looks it would smell!

You should have an air filter in place in between the plenum and coils but filters are generally flimsy and cannot catch all particles.

Air filters also need to be changed regularly.

How To Clean Mold In Your Air Conditioning

If there is really a big build up of mold growth within your HVAC system, you should probably have a licensed professional do it.

If you just have simple surface mold on registers like this:

You can just clean it yourself with a mild detergent.

It's not just mold that can be present in your HVAC system and ductwork:

Through normal occupation in a home, we generate a great deal of contaminants and air pollutants, such as dander, dust, and chemicals. These contaminants are pulled into the HVAC system and re-circulated 5 to 7 times per day, on average. Over time, this re-circulation causes a build-up of contaminants in the duct work.

While dirty ducts don't necessarily mean unhealthy air in your home, school or workplace, they may be contributing to larger health issues or harboring contaminants that could cause serious problems for people with respiratory health conditions, autoimmune disorders or some environmental allergies.


How To Get Rid Of The Mold Smell

Getting rid of the mold smell in a home home can be accomplished by a process known as mold remediation. Mold remediation will get rid of the odor by not only removing the mold damaged materials, but also sanitizing the home through a process called micro-cleaning.

In most cases, this will need to be done by a licensed professional. Here's a great guide to determine whether you need mold remediation or you can do it yourself.

Once mold remediation completed, the odor should be gone.

If the smell still lingers within the home it could indicate all the mold has not been removed.

Dead mold spores can house itself in your carpets, mattresses and other furnishings which may need to be treated or discarded.

Your clothes in most cases can be put in a traditional laundry machine. Sometimes it may be necessary to put the clothes through two cycles.

Click Here For The Complete Guide To Remove Odors From The Home

What Else Can Cause A Musty Odor In The Home


As a mold assessor, the number one culprit that I find is causing musty smells in homes during a mold inspection is:

High humidity

Humidity is how the amount of water vapor measured in the air.


Humidity itself can lead to mold growth on both hard surfaces


Mold generally will only be on the surface of hard surfaces and in most cases but may let off what people describe as a mildew smell.

High humidity for an extended period of time could lead to mold growth on porous items such as couches, beds, clothes, etc.

There are many times however by just controlling the humidity within the home that the smell will vanish. The smell of dampness is mostly related to humidity.

What Causes High Humidity In The Home?

Think back to that locker room smell again (I know, sorry!)

What happens in that locker room besides horseplay by kids?

Showering, or so we can only hope!

Well hot showers can create high relative humidity within bathrooms. If the bathroom isn't ventilated properly this can create a dew point.

Bathrooms can be a prime source of high humidity, but most bathrooms are built to withstand it.

One of the main causes of high humidity is an air conditioning unit that is not properly functioning. If your air conditioning is not dehumidifying properly it could also be a sign that is it undersized or oversized.

How To Fix Humidity Problems In The Home

A home that has high relative humidity problems indicates there is a problems with the HVAC system, ventilation or poor living habits such as running the air conditioning with the windows open. A licensed HVAC contractor or engineer may need to be contacted.

But that sounds expensive, right?

Well… another option is:

Get an external dehumidifier. This is especially good if you are just having a humidity problem in one section of the home.

External dehumidifiers can work great and don't necessarily need to be ran 24 hours a day. You can run it for a few hours in a room while you are somewhere else in the home and it can make a big difference.

The downside about external dehumidifiers is they need to be emptied because they fill up with water pretty easily.

To prevent humidity problems that can lead to condensation, you should also make sure the air conditioning is set to the "Auto" position and not "On". You will really start to see mold growing on your clothes if you do this.

Other Issues Than Can Cause Odors In Your Home



I know we all love our four legged friends but the reality of the situation is that sometimes as owners we tend to maybe not keep as much as necessary with their hygiene.

And sometimes, even if you do keep up, they will still have an odor. It's just the way it goes.

Keep in mind they also due "bathroom activites" only it's not generally done in the bathroom.

If you have cats, litter boxes is where the cats will have their poopy party! Litter boxes need to be changed after everytime your cat uses it.

Sometimes the odors that is caused by pet dander in the home can be confused with a musty odor.

Getting Rid Of Pet Odor

If your pet has it's own bed or place to lay, make sure it is washed on a weekly or bi-weekly basis. Get them a bed where the outside cover can be put in the washing machine

Vacuuming on a regular schedule can also remove a build up of pet dander.

Air purifiers with a HEPA filter are also a good way to remove pet dander from the air. It's an investment well worth it not only for pet odor removal but overall air quality.

Garbage Compactor

Mold can often grow on decomposing food which can produce a foul odor. It goes without saying that you need to get rid of your indoor garbage frequently.

But often the forgotten part of the puzzle is your garbage compactor.

If you don't turn it on after putting old food or even liquid down there and odor and start to form. Many times people will confuse this with an moldy smell in their home.

How To Get Odor Out of Your Garbage Compactor

For one, make sure you turn on the garbage compactor in the sink and not just let food sit in there for an extended period of time.

Pouring Pine Sol in the sink will also help get rid of this odor.

Cigarette Smoke

Although the odor of cigerrettes is pretty distinct, once the smell fades a little there are people that may confuse this musty odor with mold. Even if not confused with mold, the odor can be pretty overwhelming.

But why does cigarette smell linger in the house for a long period of time?

It's because the chemicals that are in the smoke seep very deeply into porous items throughout the home.

Out of all the odors, cigarette smoke may be the hardest to get rid of.

How To Get The Smell Of Cigarettes Out Of The Home

There are many steps you can take to remove the odor but it may need to be done more than once.

If you have an active cigarette smoker living with you…

Good luck with it!

It's probably best to follow these instructions if you are starting from scratch in a new house.

Step 1:

Get rid of all carpets, rugs and any other extremely porous furnishings in the home. Such items as mattresses may be virtually impossible to get the smell out.

Step 2:

Prime and paint all the walls and ceilings in the home. Fiberlock Shockwave or Killz Odor Removal paint can really help when used as a primer.

Step 3:

Treat the HVAC coils and ductwork with a biocide. Acid washing the coils may also help. I suggest using Vital Oxide as this can really help remove odors.

Step 4:

Wipe down all cabinets and vanitys. I suggest damping a wash cloth with Vital Oxide for this as well.

Moth Balls

Everytime I got into a home and smell moth balls I just shake my head.

Moth balls are made of pesticide that are deodorized which people use to protect against mold smell and other odors, but unfortunately this has many side effects. Moth balls used as an smell removal for mold is not an effective form of odor removal and should not be used.

For one:

Mothballs have an odor itself which can sometimes resemble mold or may even smell worse.

Yes, moth balls can help keep moths away but it can also cause adverse health effects in humans. This is especially true for humans with a compromised immune system.

And if you have dogs and cats, it can also be toxic for them.

How To Get Rid Of Moth Ball Smell

Getting rid of moth ball smell in the home can be a nuisance but possible in three easy steps:

Step 1:

Remove the Moth balls from the area

Step 2:

Air out the home by opening the windows and doors

Step 3:

Wash all carpets

Step 4:

Lightly mist an odor remover such as Vital Oxide into the air


Getting rid of moth ball odor in your clothes may not be so simple. One hack that works real well is to wash your clothes with one cup of vinegar.

Stagnant Air in The House

Stagnant air can sometimes be confused with mold. Air flow within a home is extremely important. If there have been no doors or windows open and the HVAC system has not been running for a substantial period of time, this can lead to an odor.

Each home needs many air exchanges per day.

If you walk into a home that hasn't been accessed for at least a few weeks with a minimal amount of air exchanges you will get a whiff when walking through the front door.

Indoor Plants

Indoor plants should realistically be outdoors…

But hey! If you want your indoor plant by all means go for it.

There are actually plants that can improve indoor air quality such as the Areca Palm.


Some indoor plants can be a source for an earthy odor because you have to water it.

Make sure if you have an indoor plant you have a non porous pan for it to protect the floor covering from getting water damaged.

Ozone To Remove Smell

Ozone generators have become popular removing indoor odors in recent years. It has been said to be very effective according to manufacturers of the product. There is no scientific evidence to back this up and can be harmful to humans when inhaled or ingested. Additionally, no government agency recommends this be used in a location when occupied.

If you use an Ozone generator that states it's EPA approved, this can be misleading. The EPA states this about Ozone:

Several brands of ozone generators have EPA establishment number on their packaging. This number helps EPA identify the specific facility that produces the product. The display of this number does not imply EPA endorsement or suggest in any way that EPA has found the product to be either safe or effective.

Please Note: EPA does not certify air cleaning devices. The Agency does not recommend air cleaning devices or manufacturers. If you need information on specific devices or manufacturers.


If you decide to use Ozone to remove odors in the home, make sure you are not staying there!

Air Purifiers To Remove Mold Smell and Other Odors

Air purification systems are a great way to combat musty odors in the home. Keep in mind that not all air purification systems are the same. Some are better than others.

Air purifiers work by not just covering up odors with some kind of fragrance, but removing the actual contaminents in the air that cause the odor in the first place.

But how does it do that?

Basically, long story short, it uses negative air to take in airborne particles through a serious of filters. The air purifier then traps the contaminents in a filter or destroys it altogether. It really depends on what type of air purifier you have.

These are some of the most common type of air purifiers you can get:

HEPA Filter Air Purifier

This is probably the most common type of air purifier.

HEPA stands for high-efficiency particulate air. A HEPA filter is a type of mechanical air filter; it works by forcing air through a fine mesh that traps harmful particles such as pollen, pet dander, dust mites, and tobacco smoke.


HEPA filters are the are used during the mold remediation process as well to remove mold spores in the air.

These type of air purification systems definitely help when trying to remove mold smells from the home, but ultimately the source of the odor will need to be removed first.

Activated Carbon Air Filter Purifier

Activated Carbon Air filter purifiers aren't necessarily better or worse than HEPA filters, just different. Activated Carbon air filter aren't designed to remove airborne particles like mold. It is designed to get rid of odors and it does that very well.

Specifically for cigarette smoke.

If you ever tried to get rid of that smoke odor, it is a challenge to say the least. Air purification systems that use activated carbon air filters do just that better than any other type of air purifier.

There are many air purification systems that have both Activated Carbon air filters as well as HEPA filters. Best of both worlds.

UV Light Air Purifiers

UV lights are commonly used in home air conditioning units over the past ten years or but there are stand alone air purification systems that use UV lights as well.

UV lights can kill airborne viruses, germs and bacteria, however…

UV light air purifiers is not going to do much for you in terms of removing odor and works best as an add on to a HEPA filter air purifier or Activated Carbon Air purifier (or both).

HVAC Air Purifiers

There are different kinds of air purifiers that can be added on to your air conditioning system. The most common recently is called the REME Halo.

This is how the REME Halo works:

The REME HALO is an in-duct air purifier that uses RGF's Reflective Electro Magnetic Energy technology. It is installed in the supply side plenum of the HVAC system. This technology produces hydro-peroxide plasma and uses ultra-violet light to purify surfaces and the air inside your dwelling.

It is different from other indoor air quality products in that it is not passive. It is not something that works to catch pollutants but is designed to actively go to where the contaminant is and eradicate it. The charged particles this device creates cause pollutant particles to stick together making them larger at the molecular level. Because they are larger, air filters have a better chance of trapping them as they pass through.


How Are You Getting Mold Odors Out Of Your Home?

Is there a specific method you used to remove the mold smell and other odors out of your home?

We want to hear from you.