There are many signs that can indicate you may have a mold problem in a house. Whether you see it, smell it or can feel it in the air, at the least mold is unsightly, and at its worst, it is destructive and can cause serious health issues.
Below we’ve outlined the most common signs of mold in a home, regardless of the cause of the mold in the first place.
Important: Concerned you have a mold problem? A mold detection kit or service from a qualified professional can discover if mold is present as well as its severity – even when it isn’t visible.
Without even doing a mold test, there are three main signs and symptoms of mold in a house: visible signs of mold, a musty or moldy odor and health symptoms.
Visible signs of a potential mold problem in a house
- Black growth on tiles or grout
- Loose or lifting drywall tape
- Paint that is peeling or cracked
- Persistent condensation
- Surface biological growth
- Wood that is warped or lifting
- Discoloration or water staining on walls
Scent, smells and sensations indicating the possible presence of mold
- Feeling of dampness in the air
- Mildew smell indoors
- Musty odor when air conditioner or heat is running
Health symptoms observed when in contact with mold
Visible signs of mold in a home
One of the most common ways mold is discovered in a home is by simply seeing it. Here are some of the more common signs that black mold is present in a house.
Black Mold growth on bathroom tiles or grout
One of the most common places that mold is found is in bathrooms. The increased moisture and common presence of tile in bathrooms are each highly conducive to the proliferation of mold colonies.
Mold is often found behind tiles as well as in tile grout which is the material in the gaps between tiles. Grout is porous, meaning it has tiny holes or cavities which that water can penetrate. Other reasons why mold grows in grout is that dirt and other material also find their way into the grout.
While sealant can provide some amount of protection, over time both tiles and grout expand and contract. That creates larger voids in the grout and between the grout and adjacent tiles. When left in this state pieces of grout break and fall off entirely.
At that point, mold can penetrate beneath the sealant barrier and move through the grout and behind tiles.
Loose or Lifting drywall tape
This is a sure sign that moisture has infiltrated the wall.
Paint that is cracked or peeling
When paint is visibly cracking and peeling the underlying issue is often a buildup of moisture under the paint. While cracking and peeling don’t mean there is definitely a mold problem, if moisture is found behind the paint, mold often accompanies it.
Once mold is growing behind the paint, it often makes its way into the wallboard and even the studs and structure behind the wall.
Tip: When mold has been painted over, the paint often bubbles or flakes off as the mold makes its way back to the surface.
In high humidity environments condensation forms on windows, pipes, walls and other surfaces. This water buildup encourages mold growth. The problem can go beyond the surface where water is beading up if it is dripping or pooling on other surfaces.
When humidity-borne water is found, check the surrounding materials for signs of water damage and mold, too.
Surface biological growth
There are many kinds of mold. Visually, mold can be found in many different colors including black, grey-brown, grey-green, white, white with orange splotches and pink to name a few.
Toxic black mold (Stachybotrys) is usually dark in color and can also take the form of a slick or slippery green-black growth.
Dark or damp areas are the most common places where toxic black mold (and other mold) is found.
Warped wood trim or paneling
Warping wood is usually the result of prolonged exposure to humidity or moisture. The warped wood itself as well as adjacent surfaces should be checked for mold.
Water stains or discoloration of walls and Ceilings
Yellow and/or gray stains on wall and ceilings are a sign of moisture build-up. In more obvious cases, where mold growth may have been growing for an extended period of time, the wall or ceiling surface may have a brownish, greenish, blackish or other dark discoloration.
The color that is present is often a clue as to what species of mold.
You may also notice places where the paint is coming off due to moisture, or where it is “bowing” out.
One way to check for mold growth is to move a medical grade, fluorescent tube (usually called a blacklight) around and inspect walls, ceilings, and even carpets while it is dark. Under black light a yellow glow is a sign of mold growth.
Scent, smells and sensations where mold is present
Once you’ve smelled mold, you won’t soon forget it. Mold has a mildewy, musty smell that is often present in areas where mold is actively growing. It’s one of the tell-tale signs of mold in a home.
Dampness in basements or crawl spaces
Next to bathrooms, basements and crawl spaces are among the most common places to find mold. Both environments lack ventilation and active air circulation.
Depending on where the home or building is located, they may also experience colder ambient temperatures compounding the issue.
Cooler temperatures encourage condensation, and condensation means moisture.
Another reasons why crawlspaces and basements are good breeding grounds for mold is simple lack of visibility. These rooms aren’t visited nearly as much as other rooms indoor. So, water buildup and mold are often left to grow for extended periods of time before eventual discovery.
Mildew smell or musty odors in rooms
Odors can often be the first or only sign of a potential mold problem, since mold commonly propagates in places not normally in view. This does not necessarily mean that you definitely have a mold problem, but it should prompt you to look for the other signs, or to look for the mold growth itself (How to Find Mold).
Musty odor when air conditioner or heater (HVAC) is run
In some cases, mildewy smells will only be evident when the air conditioning or heat is turned on, or it may just be much more evident when the HVAC system is running.
When running A/C or heat is tied to those musty smells, the HVAC system itself may be the location of the mold infestation. Check the heating and cooling components themselves as well as the ductwork.
Health symptoms indicating mold’s presence
The health symptoms below may indicate exposure to mold. Many of the symptoms can also be caused by other factors, however.
Allergic reaction or respiratory symptoms
The most common symptoms experience in the presence of mold are allergic reactions and other respiratory-related issues. It’s often all but impossible to know if these symptoms are being caused by mold or other allergens or conaminants.
But, it is worth noting that a Mayo Clinic study from 1999 stated that mold is the culprit in nearly all chronic sinus infection cases. In the United States, there are 37 million cases annual (or more).
Avoiding the negative effects of working in a moldy environment are why workers often wear mold respirators and mold masks when performing mold remediation.
Learn more about the health risks of mold exposure.
Signs of toxic poisoning from VOCs
Fungi, including toxic black mold and other mold varieties, produce Volatile Organic Compounds (VOCs) as they break down substances. The VOCs are what causes the moldy/musty smells which are often described in mold-ridden environments. Exposure to high levels of VOCs may irritate the mucous membranes and the central nervous system leading to symptoms of headaches, decreased attention span, difficulty in concentration, and dizziness.