8 Signs There May Be Mold and Mildew in Your House

Mold—the dreaded “M” word that no one wants to hear (or see, or smell, etc.). The presence of mold can stop a home sale in its tracks or lead to some major homebuyer regret later on. 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’s going to cost to remove it. But, mold can be sneaky, making it hard to find if you don’t know exactly what you’re looking for.

“Mold growth typically occurs in out-of-sight wall cavities as a result of water damage from flooding or leaks,” explains Darren Hudema, director of training and technical services at PuroClean, which provides mold and water damage remediation services. “Before you know it, mold creates a toxic environment in your home, compromising the quality of the air you are breathing in every day.”

But what causes mold?

To thrive, grow, and multiply, mold requires four ingredients, Mike Powell, professional engineer, mold assessor, mold remediator, certified home inspector, and owner of Red Flag Home Inspection, says. Those “ingredients” include mold spores (which are always floating around in the air), a temperature range suitable for mold growth (it grows fastest between 77 and 86 degrees Fahrenheit), organic or carbon-based material on which mold can grow (like wood, drywall, paper products, carpet, etc.), and, perhaps the most well-known culprit: moisture.

Unfortunately, Powell says it’s nearly impossible to control all of these factors at once. 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.

Since mold tends to grow in high-moisture areas, there are certain places where you’re more likely to find it. “The most common areas are basements, bathrooms, kitchens, poorly ventilated rooms, crawlspaces, or other areas of high humidity and dampness within walls and pipes,” says Hudema. Knowing where to look is a helpful first step toward being able to recognize the signs of mold or mildew in your home.

Mold vs. Mildew

Before we delve into the mold and mildew signs, we need to clear up a misconception. Michael Rubino—mold and air quality expert, author of The Mold Medic, and founder of HomeCleanse, an air quality services company—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. Using a good bathroom cleaner, for example, can help keep surface mildew at bay. In fact, Rubino says some types of mildew, such as Aspergillus, are common mold 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,” he says. Choose a mold remover that is compatible with the surfaces you intend to clean.

Now that we’ve cleared that up, below are the signs that you may have mold and mildew in your home.

Moisture or condensation on walls and windows

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’re noticing a little bit of this (especially in the winter season), that’s not an immediate cause for alarm. However, Tim Swackhammer, founder and CEO of Mold Medics in Carnegie, Penn., says that an excessive amount of 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,” he says. “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, he says this can trap moisture inside the walls.

Visible mold

Sometimes you can actually see mold, making it one of the easier 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,” he explains. The most common colors of mold are gray, black, and green, but it 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 in color.

Rubino recommends grabbing a flashlight and regularly checking these areas for signs of mold:

  • 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. In fact, 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 all day long. (You can purchase a humidity meter to check and monitor the levels in your home.)


Compared to an impossible-to-miss water issue, like a burst pipe, a small leak may not sound like that big of a deal. But, a slow leak, like that from a kitchen faucet, can quickly become a bigger problem—and lead to mold. When appliances are leaking, the water can soak into the cabinetry or leak to the flooring below, causing a buildup of moisture, warns Jake Romano, manager of John The Plumber, a residential service plumbing company in Etobicoke, a suburb of Toronto.

“The same can also be said about a leaking P-trap under your kitchen or bathroom sink,” he adds. Although these are easy-enough fixes, Romano says the problem is that a slow leak can often go unnoticed for a while—especially if you store a lot of items under the sink that you don’t use everyday—and this gives the mold more time to grow.

So make sure to check these areas often, and act quickly if you notice any dampness.


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, franchise owner of AdvantaClean, a water damage and mold restoration service.

In addition, 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 the growth or mold. “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—president at environmental services and consulting company Healthy Building Science and home maintenance company Home Stewards—when there’s been a single leak or other type of water damage, there will usually be one line that formed 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.

Musty smell

Sometimes, you’ll smell mold before you see it. “Many times, mold is growing somewhere that is very difficult to see, like the underside of sheetrock walls, or under carpeting, et cetera,” says Tony Abate, a certified mold inspector and vice president and chief technical officer at AtmosAir Solutions in Fairfield, Conn. “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,” he explains.

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.”

Bubbling or peeling paint

Sometimes bubbling or peeling paint is just a sign that you didn’t prep well before painting, you didn’t use the best painting techniques, or, maybe your home just has a very old paint job. However, Powell notes that this could also be a sign of 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,” he 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,” he says.


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.”

Physical or medical symptoms

Unfortunately, mold can cause a variety of health problems. “Mold can cause infections, allergic reactions, and toxic effects in some individuals, but the clinical effects can vary from person to person,” says Kelly Johnson-Arbor, M.D., medical toxicologist and co-medical director at the National Capital Poison Center in Washington, D.C.

“For people with intact immune systems, mold can cause—or worsen—allergic reactions and asthmatic symptoms, such as shortness of breath, wheezing, and coughing,” she tells us. “Fungal infections, which can involve the blood, brain, lungs, or other organs, are more common in people with weakened immune systems.”

As mentioned above, 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 says.

It’s also worth noting that the fungus Stachybotrus chartarum (often called “black mold”) was once thought to cause serious medical conditions including pulmonary hemorrhage, though there is currently a lack of evidence linking it to serious medical conditions in most people.

Still, mold can be a risk to to the health of yourself and your home. That’s why 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 to capture small allergenic spores,” he says.