The Complete Guide to Mold in the Home

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How can such a small thing create so much trouble?

If you’ve ever experienced moisture issues inside your home, you’ve probably battled mold as a result. Mold is a naturally occurring organism that can be found anywhere, but when it makes its way inside your home, it can create a lot of problems.

Outside, mold is needed to break down dead materials. Mold spores are tiny and lightweight, and travel easily through the air. Many people are allergic to mold, though, and when it grows indoors, it creates microbial air pollution.

Some types of mold are even deadly.

Environmental testing expert Robert Weitz says that mold multiplies at an extraordinary rate and will break down or consume whatever it sticks to.

Sheetrock, according to Weitz, is a good example of this. When sheetrock gets wet, mold can attach itself to the paper inside and cause it to deteriorate. Eventually, it attaches to the wood underneath and causes widespread rot. When that happens, the moldy areas have to be cut out because it’s impossible to remove.

Mold orange

According to the CDC, mold can enter your home through open doorways, windows, vents and heating and air conditioning systems. Molds flourish with moisture — that includes areas around leaks in roofs, windows or pipes, or where there has been flooding. It can grow in dust, paint, wallpaper, insulation, drywall, carpet, fabric and upholstery.

In this guide, we’ll take a look at how mold can impact your health, what kind of molds are the most common in your home, and how to prevent mold from spreading. We’ll also look at how you can treat mold yourself, although a professional should be consulted if the contaminated area is more than 10 square feet.

Health implications

The World Health Organization says that exposure to microbial mold spore contaminants is clinically associated with respiratory symptoms, allergies, asthma and immunological reactions. Upper and lower respiratory illnesses are the most common responses to mold.

Other health issues can include breathing difficulties, skin rashes, headaches, cough, wheezing and asthma, according to Weitz. Some molds can cause deadly reactions in people.

If you’ve been exposed to mold for a prolonged period of time, symptoms can also include chronic fatigue, cold- and flu-like symptoms, shortness of breath and weakness.

Four types of common molds — and one scary one

There are hundreds of thousands of different subspecies of mold that take up residence in your home. The first four listed here are the most common, and the fifth is one that can cause serious health problems when it’s present inside homes.

Image of mold in petri dishes

#1 Penicillium

Penicillium molds include about 200 different species. This is the species that gave us the first antibiotic: penicillin. These molds are naturally found in soil, decaying vegetation and air, and are common contaminants on various substances, according to the Mold and Bacteria Consulting Laboratories.

Penicillium chrysogenum is the most common species in indoor environment, according to the MBL, and can live on anything — damp building materials, walls, carpets, mattresses and furniture dust.

Health concerns: Like most molds, Penicillium molds can trigger an allergic reaction because of their toxicity. Some subspecies make food inedible and even dangerous, like when an orange has a layer of greenish white fuzzy mold. Other subspecies are actually a part of food — think of cheeses like Roquefort, Camembert and Stilton.

What to look for: If you’ve ever left food in the refrigerator too long and seen it grow fuzzy and blue, penicillium is probably one of the molds causing it. They produce enormous quantities of green, blue or yellow fuzzy spores.

#2 Cladosporium

Cladosporium includes more than 500 species. They are considered secondary wall colonizers and are the most widespread molds. These grow most often on carpets, curtains, upholstery, and wallpaper, and can also grow on window sills and plywood.

They appear in clusters of black, yellow, or green spots and spread quickly.

Health concerns: Aside from respiratory issues, Cladosporium molds can cause eye and ear infections, skin problems and sinus infections. Other symptoms of an allergic reaction are dry skin, sneezing, a stuffy or runny nose, coughing, postnasal drip, and itchy eyes, throat and nose.

What to look for: Cladosporium appears in clusters of black, yellow, or green spots. The spots spread quickly when not cleaned away.

#3 Alternaria

There are around 50 species of Alternaria. This mold shows up in damp areas like the sink or shower but can also thrive on old food. It is a major plant pathogen.

Health concerns: This mold is most commonly associated with asthma. Studies have shown that this mold is present in many homes, with the highest concentrations on living room floors. Although asthma symptoms are more common when exposed to Alternaria outside, indoor exposure affects people as well. A study published by the National Library of Medicine said that “the odds of having asthma symptoms in the past year increased significantly with higher indoor levels of [Alternaria] antigens.”

What to look for: Alternaria grows in thick colonies that are usually green, black, or gray. It’s darker color can confuse homeowners into thinking it’s “black mold.”

#4 Aspergillus

Like other molds, this one has lots of subspecies. Some species can produce mycotoxins, which are, as the name implies, toxic.

The MLB says Aspergillus can be anywhere, and can be stirred up when vacuuming, for example. It is also found on damp walls, wallpaper, PVC/paper wall covering, gypsum board, floor, carpet and mattress dust, upholstered-furniture dust, acrylic paint, UFFI, leather, HVAC insulations, filters and fans, humidifier water, shoes, leather, bird droppings and potted plant soil, plastic and decomposing wood.

Health concerns: One species, Aspergillus fumigatus, is actually a human and animal pathogen and can cause Aspergilloses, a disease of the lungs.

According to the Merck Manual, a ball of fungus fibers, blood clots, and white blood cells may form in the lungs or sinuses when a person has Aspergillosis. People may have no symptoms or may cough up blood or have a fever, chest pain, and difficulty breathing.

What to look for:  Different species of Aspergillus are different colors. This is a tough one to identify visually.

#5 Stachybotrys chartarum — “black mold”

This is the mold that everyone is most afraid of. It’s associated with heavy water damage. It grows most often on wet cellulose, like building materials including wallboard, ceiling tiles and cardboard.

Not all molds that are black are Stachybotrys, and reports surrounding the dangers of “black mold” may have been overstated.

Health concernsThe American Society for Microbiology says there hasn’t been well-substantiated supportive evidence of serious illness due to Stachybotrys exposure. At one point, Stachybotrys was blamed for a case in Cleveland where 10 infants were diagnosed with idiopathic pulmonary hemorrhage. While initial studies linked black mold with IPH, the CDC later retracted their support of the study because there just wasn’t enough evidence.

The biggest argument against this mold causing things like debilitating respiratory symptoms, immune dysfunction and cognitive impairment is that it is never present in the amount it would require to have such an adverse effect, according to a 2008 report in Toxicological Sciences journal.

What to look for:  This mold is truly black, with no other colors present.

How do I know if there is mold in my home?

Black mold on the walls of a home

You can’t always see or smell mold, especially if it’s behind paneling. Some indications that you have a moisture problem include rusty pipes and warped walls. Remember that recurring moisture or dampness attracts mold, so if you’ve had issues with water and are concerned about mold, get your home tested.

Mold smells musty, so try to track down the source of the odor. If you can’t find it easily, it could be under the flooring or in the walls.

Unexplained respiratory issues are also an indicator.

Mold kits are available at hardware stores and online and are able to detect mold. Viable mold kits detect mold in the air — as opposed to surfaces — and cost between $20-$45. You can send the results off to a lab for an additional $40-$70 to determine what type of mold it is, but that isn’t really important, according to the CDC. What’s important is cleaning it up and fixing the issue.

The EPA does not endorse any type of mold testing kit and recommends hiring a professional. Even though a mold kit may confirm you have mold, it can’t tell you where it is, according to the University of Kentucky’s Cooperative Extension Service. Kits also commonly give false negatives and false positives.

How do I decrease mold in my home?

You can’t completely avoid having mold indoors. But, you can take precautions. According to Luke Armstrong, an expert in mold removal, mold growth isn’t always visible when it appears in homes. It can grow behind walls and ceilings and other hidden areas.

That’s why prevention is so important.

Two main things contribute to mold overgrowth: moisture and oxygen. Mold also really likes cellulose, which includes organic material found in wood, drywall, insulation and other building materials. Cellulose combined with moisture allows mold to grow.

The CDC recommends the following steps to prevent mold:

  • Keep humidity levels as low as you can — no higher than 50 percent — all day long. An air conditioner or dehumidifier will help you keep the level low, according to the CDC.
  • Be sure the home has adequate ventilation, including exhaust fans in the kitchen and bathrooms.
  • Mold inhibitors can be added to paint, which can help reduce mold growth.
  • Clean bathroom with mold-killing products.
  • Do not carpet bathrooms.
  • Remove and replace flooded carpets.

How do I treat mold in my home?

Mold on the ceiling of a home

If you have a leak, or if your home was damaged by flooding, repair the water source and dry everything out as well as possible. A dehumidifier can help in areas that are chronically damp, like basements.

If mold is a problem in your bathroom, you may need to increase the ventilation. And that’s not just limited to bathrooms — starting in the 1960s, builders started building homes and commercial buildings that were more tightly sealed. While that’s great for power bills, it prevents moisture from easily escaping.

Mold growth can be removed from hard surfaces with soap and water or a bleach solution (no more than 1 cup of household laundry bleach in 1 gallon of water).

Don’t ever mix bleach-based cleaning products with ammonia-based products. That creates a toxic mix that’s dangerous if you inhale it. Check the ingredients listed on all household cleaners.

If you smell mold but don’t see any, look for places it might be hiding. That can include behind wood paneling and wallpaper, above ceiling tiles and the underside of carpeting, according to the Environmental Protection Agency. It could even be beneath roof shingles if there has been a leak.

Use a wet vacuum if you’re cleaning out a wet area that already has mold. That will pull most of the water out, but be sure to clean all the vacuum parts completely when you’re done to remove all the mold.

Any contaminated area that’s larger than 10 feet should be handled by a mold remediation company, according to the EPA. There’s a risk of spreading the mold when you clear out materials like wall board, paneling or ceiling tiles. You’ll probably spread more mold spores when you remove it, so the area needs to be sealed off while decontamination is taking place.

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