Mold: That dreaded “M” word no one wants to hear (see or smell). The presence of mold can stop a home sale or lead to major homebuyer regret. And if you’re living in a home with mold, you’re probably wondering how it’s adversely affecting you and your family’s health—and how much it will cost to remove it.
But mold can be sneaky, making it hard to find if you don’t know exactly what to evaluate. Here, home and mold experts share the typical signs of mold in the house to help you identify if there’s an issue. Plus, learn the difference between mold and mildew and how they happen in the first place.
What Is Mold?
Mold is a fungal growth, not bacteria. It’s a natural part of the environment and reproduces by spreading spores in the air—indoors and outdoors. When outdoors, mold helps break down dead organic material (like fallen leaves), but indoors, mold can become problematic and cause health problems for your family. Let’s look into what causes mold and where it typically grows.
What Causes Mold
To thrive, grow, and multiply, mold requires four elements, says home inspector Mike Powell. Those components include:
- Mold spores: Unfortunately, these are always floating around in the air.
- Temperature: Mold needs a temperature range suitable for growth, and it grows fastest between 77 and 86 degrees.
- Material: Organic or carbon-based materials allow mold to grow (like wood, drywall, paper products, carpet, etc.).
- Moisture: This is perhaps the most well-known culprit of mold growth.
Sadly, Powell says it’s nearly impossible to control all mold factors simultaneously. After all, mold spores are everywhere around us. However, focusing on sources of moisture is your best bet at preventing or removing mold. As Powell explains, if you can limit the moisture, you can limit the mold.
Where Mold Grows
Since mold tends to grow in high-moisture areas, there are certain places where you’re more likely to find it. Knowing where to look is a helpful first step toward recognizing the signs of mold and mildew in your home.
“Mold growth typically occurs in out-of-sight wall cavities as a result of water damage from flooding or leaks,” explains Darren Hudema of PuroClean. “The most common areas are basements, bathrooms, kitchens, poorly ventilated rooms, crawlspaces, or other areas of high humidity and dampness within walls and pipes. Before you know it, mold creates a toxic environment in your home, compromising the quality of the air you are breathing in every day.”
- Attics
- Basements
- Crawlspaces
- Grout and caulk
- Window sills and door frames
- Underneath sinks
- Carpeting
- Appliances
Mold can also grow behind wallpaper or inside the walls. “The main visible sign of mold growth is the discoloration of the wall; even if you paint over it, mold will persist and continue to show signs on the surface,” Rubino warns.
In addition to structural elements of the home, mold may be growing on individual items as well. “Mold growth could occur on leather shoes or garments, clothes hanging in the closet, and on the backside of furniture against the wall where other moldy items are,” Powell explains.
That’s because closets tend to be small enclosed spaces with no air-conditioner supply vents. Powell adds that closets may often have humidity levels higher than the adjacent living space. According to the CDC, humidity levels in your home should be no higher than 50 percent throughout the day. (You can purchase a humidity meter to check and monitor the levels in your home.)
Mold vs. Mildew
Before we delve into the mold and mildew signs, let’s clear up a misconception. Rubino tells us that most people believe they may have mold or mildew, but mildew is actually a type of mold, not a separate entity.
“The term ‘mildew’ basically refers to mold that’s light in color and powdery in texture, and these mold colonies could be gray, white, or light green and grow in a flat format without much height, meaning they aren’t as fluffy and sponge-like as some other mold growth,” Rubino explains.
Since mildew grows on the surface, it can be easier to remove than burrowing mold, but it should still be taken seriously. Rubino says some types of mildew, such as Aspergillus, are common molds that can create toxic mycotoxins.
“This is why mildew is no less of a home health threat than other varieties of mold and should be treated quickly and correctly,” Rubino says. Choose a mold remover compatible with the surfaces you intend to clean. For example, a good bathroom cleaner can help keep surface mildew at bay in places like the shower or tub.
Signs You May Have Mold in Your Home
Now that we know what causes mold and the difference between mold and mildew, here are the most common signs of mold in the home.
Moisture or Condensation
If there’s water on your walls and windows, it’s usually the result of humid air coming into contact with a cold surface. If you notice slight condensation (especially in the winter months), that’s not an immediate cause for alarm. However, Tim Swackhammer of Mold Medics says excessive moisture or condensation can be caused by too much humidity in your home—and that’s something to look out for.
“Generally, we see condensation occur first on windows, on ductwork or registers, and in corners of exterior walls,” Swackhammer explains. “It shows up in these places for the same reason: They are colder than other surfaces in the home, and in all of these cases, it’s a sign that you may hold a mold problem because condensation equals moisture equals mold.”
Hudema adds that moist drywall provides the perfect home for mold. Whether the basement has been flooded or you have a leaky pipe, this can trap moisture inside the walls.
Visible Mold
Sometimes, you can physically see mold, making it one of the easiest indicators that you have a problem. “There are over 100,000 species of mold identified around the world so far, and with so many in existence, mold can come in a variety of colors, shapes, and textures,” Hudema explains.
The most common colors of mold are gray, black, and green, but mold can also be white, pink, blue, red, purple, brown—and sometimes a combination of colors. “As for textures, [mold] could be fuzzy, powdery, velvety, or slimy,” Rubino says. Mildew (as explained before) is flat, powdery, and typically gray or white.
Leaks
Compared to an impossible-to-miss water issue (like a burst pipe), a small leak may not sound like a big deal. But, a slow leak (like that from a kitchen faucet) can quickly become a bigger problem—and lead to mold. When appliances leak, the water can soak into the cabinetry or spread to the flooring below, causing a moisture buildup, warns Jake Romano of John the Plumber.
“The same can also be said about a leaking P-trap under your kitchen or bathroom sink,” Romano adds. Although these are simple fixes, Romano says the problem is that a slow leak can often go unnoticed for a while—especially if you store many items under the sink that aren’t used often—which gives mold more time to grow. This is why you should frequently check these areas and act quickly if you notice any dampness.
Moisture Stains
In addition to leaks, you may see stains on the walls and ceiling leftover from moisture. “If you have a leak from above, this will leave a dark stain on the ceiling, and chances are, there may be mold between the floor above and ceiling below,” says Lyle Nearby of AdvantaClean.
Additionally, Nearby says the air vents in the ceiling or floors may have rust or black spots, indicative of high moisture in the air system, which usually causes mold growth. “You may also have stains on the wood veneer of your kitchen and bathroom cabinets and discoloration of floor molding and sheetrock.”
If you can see visible water stains on gypsum board walls or ceilings, it is quite possible the paper backing has microbial growth. According to Alex Stadtner of Healthy Building Science, when there’s been a single leak or other type of water damage, there will usually be one line that forms around a “pool” of water.
“If it was a recurring event, such as an intermittent plumbing leak or roof leak, you will often observe ‘tide lines’ that appear like concentric rings emanating from a central point or circle,” Stadtner says.
And here’s a tip for homebuyers and renters: Stadtner says some homeowners and landlords may try to paint over previous wet spots. “However, a keen eye may detect slight variations in paint color around water damage or small variations in the drywall texture that would indicate a past problem in that area,” Stadtner adds. Consider hiring a home inspector or following a home inspection checklist to look over the property.
Musty Smell
There may be times that you smell mold before seeing it. “Many times, mold is growing somewhere that is very difficult to see, like the underside of sheetrock walls, or under carpeting, etc.,” explains mold inspector Tony Abate. “But, if you follow your nose, that odor is called a microbial volatile organic compound (MVOC), which is a gaseous substance that off-gasses that musty odor.”
Stadtner agrees, adding, “That ‘musty’ or ‘old, wet towel’ smell is really [something referred to as] mold farts—an indication that not only is there mold present, but it is wet and actively growing and multiplying somewhere within the home.”
Warped Paint
Perhaps bubbling or peeling paint is just a sign that you didn’t prep well before painting, didn’t use the best painting techniques, or that your home has an old paint job. However, Powell notes that this could also signal moisture penetration. “When moisture within a wall assembly gets to the point where you find bubbling or peeling paint, it will typically manifest itself at the base of the wall,” Powell explains.
Swackhammer notes that bubbling can also occur on the actual baseboard, as well as the wall: “Once that baseboard is removed, large amounts of hidden mold can probably be found on the drywall and the wall cavity behind it.”
Taste
Believe it or not, your favorite beverage might alert you to the presence of mold. “Appliances are at the top of the list for microbial growth thanks to the abundance of water and organic matter they use,” Rubino says. “If a funky taste pops up in items such as the coffee maker or blender, there could be mold or mildew inside.”
Spotted Clothing
If you notice black or white spots on your clothes that feel slimy or fluffy (not just an old stain), you may have mold in your home. Never throw wet or damp clothes into a hamper or store in other unventilated areas—this is a recipe for mold growth. Inspect clothing regularly and keep up with cleaning your washer.
Carpet Marks
While mold can grow in tile grout, it can also appear on carpet. Look for spots or odors on your home’s carpet or area rugs. If you find any, you’ll want to inspect underneath and any carpet padding. Using a carpet cleaner or having it professionally cleaned can help avoid mold.
Furniture Stains
Similar to your clothing and flooring, your home’s furniture can also attract mold and mildew. The porous nature of most furniture materials is to blame. But by routinely examining the state of your furniture (especially the fibers), you’re sure to catch any stains, discoloration, or fuzz indicating mold is breeding.
A/C Filter Spots
While your home’s HVAC system helps with air quality, if there’s mold anywhere within the system, it can also spread mold spores throughout the entire house whenever it’s running. If you notice a musty odor when the air conditioning is on or see black spots on the A/C filters, you could have a mold problem.
Abate recommends having the air in your home analyzed by an air-quality professional if you suspect that you have mold. “Also, pay attention to your heating and cooling and air treatment systems and use higher efficiency 2-inch to 4-inch pleated filters in your air system to help capture small allergenic spores,” Abate adds.
Be sure to use HEPA filters for your system and replace them regularly (the recommendation is every three months). You’ll also want to routinely clean the air conditioner unit and get it professionally inspected once a year.
Pet Behavior or Illness
Mold can affect your pets as much as the humans in your home. If your pets show strange behavior, they may be reacting to mold in the house—even if you’re not yet aware it exists. For example, perhaps they no longer wish to enter an area they previously loved.
Another way pets can signal mold in the home is through illness, especially if symptoms are not a sign of other conditions. Pets may exhibit stomach issues like vomiting or decreased appetite and may experience symptoms like coughing, scratching, skin irritation, and lethargy. Remember that due to the size difference, even small amounts of mold can affect pets.
Physical Symptoms
Unfortunately, mold can generate a variety of health problems for humans, too. “Mold can cause infections, allergic reactions, and toxic effects in some individuals, but the clinical effects can vary from person to person,” says toxicologist Dr. Kelly Johnson-Arbor.
“For people with intact immune systems, mold can cause—or worsen—allergic reactions and asthmatic symptoms, such as shortness of breath, wheezing, and coughing,” Johnson-Arbor adds. “Fungal infections, which can involve the blood, brain, lungs, or other organs, are more common in people with weakened immune systems.”
Molds can also produce toxins called mycotoxins. “Some mycotoxins—like aflatoxins and ochratoxins—can cause significant human disease, but the clinical effects of other mycotoxins are less well understood,” Johnson-Arbor explains.
It’s also worth noting that the fungus Stachybotrus chartarum (often called “black mold”) was once thought to cause severe medical conditions, including pulmonary hemorrhage. Currently, however, there’s a lack of evidence linking “black mold” to serious medical conditions in most people.