The 12 Most Common Types of Mold in the Home

Mold is a vital part of the earth’s natural recycling process, and because it’s so prevalent in the environment, it’s impossible to keep all mold out of a home. Mold spores travel indoors on clothing, shopping bags, and even on pets. They also sneak into a house through leaky windows and roofs. Once the invisible spores settle on a damp surface, they can begin to reproduce within 24 to 48 hours, according to the Federal Emergency Management Agency (FEMA). After Hurricane Katrina in 2005, the Centers for Disease Control and Prevention (CDC) reported that “46 percent of inspected homes had visible mold growth.”

Though some types of mold are more likely to contaminate a home than others, they all need a moist environment in which to grow. Areas that are consistently damp, such as an unvented bathroom or a sink cabinet with a leaky drainpipe, are more likely to develop mold. Researchers have identified more than 100,000 different strains of mold, but they all fit into one or more of three categories.

• Allergenic: This means they can trigger allergic reactions and asthma attacks in people who have allergies and cause slight allergy symptoms in those who don’t have allergies.
• Pathogenic: These molds usually cause symptoms only in people with immune system disorders or those who have a serious illness or are recovering from one.
• Toxigenic: These types of mold are the most dangerous and can cause serious health issues, even in healthy people.

Environmental Protection Agency (EPA) guidelines for dealing with mold recommend homeowners clean small areas on their own, but say to call in a mold remediation expert when mold growth exceeds 10 square feet or accompanies water damage. Mold remediation involves professional cleaning and removal of mold from the home. It also might involve demolition and the removal of building materials, such as drywall and carpeting, if those materials cannot be successfully sanitized. It’s also a good idea to call an expert if the mold might be a toxic variety, if the HVAC system has been contaminated with mold, or if sewage has contributed to water damage and subsequent mold growth.

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Some types of mold are more dangerous to human health than others, and the CDC warns that some people are at greater risk of health effects from exposure. Those with mold allergies or asthma might have more severe symptoms. The following 12 types of mold can be found in and around homes, whether visible or not.

1. Stachybotrys

Commonly called “black mold” for its greenish-black color, Stachybotrys is a toxigenic mold that thrives in wet conditions and is most likely to be found on cellulose-type materials, such as wood, drywall, or even stacks of damp leaves. It starts out as small black spots that become larger and spread. Stachybotrys is a dangerous mold that can cause a host of physical symptoms, including severe headaches, unexplained nosebleeds, upper-respiratory discomfort, and fatigue. It also might cause bleeding in infants’ lungs. If a family member has any symptoms and you’re concerned your home might be infested with black mold, call a mold remediation expert who can test the mold and determine the best way to get rid of it. On the positive side, many types of mold are black, but most are not actually Stachybotrys.

2. Mucormycetes

Mucormycetes are known as “filamentous” molds, because they first appear as fuzzy white or light grayish puffs with long hairs, gradually turning a deeper gray as they mature. Mucor is abundant in soil and plants, and homeowners often carry the spores inside during summer and fall. Once indoors, mucor molds like to grow on decaying fruits and vegetables, but also can grow in the condensation lines and drip pans of air conditioners. Mucor is a robust allergenic type of mold and inhaling its spores can trigger asthma attacks and difficulty breathing, even in healthy individuals. For those with allergies or weakened immune systems, inhaling mucor spores can lead to mucormycosis, a type of fungal infection that most often affects the nose, eyes, and brain. Check and clean condensation lines and drip pans monthly when running the AC and throw out old fruits and vegetables before they go bad to reduce the risk of mucor mold.

3. Alternaria

Alternaria, an allergenic type of mold, is commonly found under sinks and along tub and shower bases where wetness can linger. Experts can easily identify this mold by its velvet-soft appearance and brown filaments that resemble hairs. If you have allergies, inhaling spores from Alternaria can trigger asthma-type symptoms and upper respiratory disorders. Otherwise, the mold might not affect you. Alternaria can spread quickly, however, so if you spot it in your home, use an all-purpose cleaner that contains bleach—or one designed to fight mold and mildew—and wipe it away before it spreads.

4. Aspergillus

Aspergillus is common in many homes and is likely to grow on any damp surface, but it’s difficult to pinpoint because there are more than 180 Aspergillus mold strains and many are different colors. According to the Mayo Clinic, most strains of this allergenic mold are harmless, but a few can cause serious illnesses or result in a fungal infection known as aspergillosis in people whose immune systems are weak. Since testing is the only way to determine if the type of mold in your home is Aspergillus, your best bet is to clean away all types of mold as soon as you spot them.

5. Aureobasidium pullulans

This allergenic type of mold often is found under wallpaper when it’s stripped from the walls; it also can grow on bare wood and painted surfaces. Described as a “sooty mold,” Aureobasidium can irritate the skin if touched. When it first begins to grow, it is light pink or gray, but as it matures, it turns a deep brownish-black. Touching Aureobasidium mold and then touching the eyes or face can transfer the irritants and cause an infection. This type of mold shows up most often in humid areas, including kitchens and bathrooms, or on porous tile grout. Inhaling the spores can cause typical allergy symptoms such as sneezing and watery eyes.

6. Acremonium

Acremonium describes nearly 100 strains of toxigenic mold that can be found in the wet condensation lines and drainage pans of air conditioners and humidifiers. The mold can be difficult to diagnose without testing because it appears in several different colors, including white, pink, or gray. As the mold develops, it begins to look dry and powdery. Symptoms from exposure to acremonium spores include eye irritation, breathing problems, pneumonia, or even arthritis or fungal infections, according to the research database Antimicrobe. If family members experience any of these symptoms and you suspect your home has Acremonium mold, call a mold remediation expert to test and eradicate it.

7. Chaetomium

This allergenic and pathogenic mold is most likely to develop after water damage or flooding. Because it thrives on both humidity and darkness, Chaetomium spores often start growing within interior wall stud spaces, and might not be noticeable until the mold spreads to the wall’s exterior. By that time, the mold often has taken over large areas within the wall. Inhaling Chaetomium spores can trigger typical allergic reactions, including watery eyes, sneezing, and an itchy throat in healthy people and more serious respiratory symptoms in people with weakened immune systems. The best way to prevent Chaetomium is by quickly drying a home after flooding. Once Chaetomium spreads through interior walls, it usually requires a mold remediation expert for removal.

8. Cladosporium

Another allergenic mold, Cladosporium species prefer growing indoors in textiles, such as carpeting and upholstered furniture, although the mold also shows up beneath sinks and inside cabinets. It has a soft appearance and comes in shades of green to brown. Cladosporium usually enters the house on clothing or pets when airborne allergens are high; the spores then settle on carpeting or furniture and begin to reproduce. High indoor humidity levels increase the risk of Cladosporium growing. Inhaling the spores can cause respiratory symptoms such as a sore throat and irritated sinuses. The spores also can affect pets, causing runny eyes and sneezing. Frequent cleaning of carpeting and upholstery with a high-efficiency particulate air (HEPA) filter-fitted vacuum can help remove Cladosporium spores from a home before they start growing. Using a dehumidifier can also help.

9. Ulocladium

Ulocladium is another type of mold that usually appears after flooding or water damage. Although some strains of the mold are pathogenic, others are allergenic. The mold is black and might grow alongside other types of mold, including Stachybotrys. The two molds look alike, which can confuse non-experts. Ulocladium needs a constant supply of water to survive, so if the materials on which it is growing dry out, the mold will likely die. However, spores can remain dormant and flourish with future moisture. Allergenic strains of Ulocladium can cause respiratory symptoms that mimic hay fever, and pathogenic strains can cause serious respiratory symptoms in anyone with asthma or a weak immune system. If you suspect your home has Ulocladium mold, the best option is to consult a professional mold remediation expert, because there’s a possibility it could be the more dangerous Stachybotrys mold.

10. Fusarium

Some types of mold need warmth to survive, but Fusarium grows and spreads even in near-freezing temperatures. Strains of Fusarium can appear virtually anywhere. Most strains are allergenic, causing only hay fever-type symptoms, but a few strains can be highly toxic, leading to nervous system disorders and internal bleeding. Fusarium is a common risk to garden plants and agricultural crops, and many of today’s tomato plants have been hybridized to reduce Fusarium wilt. Indoors, Fusarium likes to grow in soft textiles, such as carpeting, upholstery, wallpaper, and drapery, and it often appears as pinkish or reddish spots. Frequent cleaning with a HEPA filter-equipped vacuum will reduce the risk of Fusarium setting up shop in your home. Homeowners who live in humid areas can use a dehumidifier.

11. Penicillium

Penicillin is a valuable antibiotic, but one strain of Penicillium mold is both allergenic and pathogenic. It produces spores that can trigger allergy-type symptoms such as sinusitis, difficulty breathing, and asthma episodes. In people with immune system disorders, the symptoms can be more severe and can lead to chronic health issues. This velvety, bluish-green mold often is found in homes that have had flooding or other types of water damage, and it needs consistent moisture to grow. Once Penicillium gets a foothold indoors, it can spread rapidly through damp wallboard, soggy carpeting, and wallpaper. An ounce of prevention is worth a pound of cure for this mold. Dry out flooded homes as quickly as possible and repair plumbing leaks promptly. Once Penicillium spreads throughout a home, professional mold remediation is recommended.

12. Trichoderma

Small puffy patches of white and olive-green mold growing in damp areas, such as near a leaky window or around a shower base, can indicate Trichoderma mold. This type of allergenic mold grows rapidly and thrives in wet spots. Trichoderma in a home can cause coughing, sneezing, and bronchial infections. The Environmental Health Center-Dallas says that some strains can produce mycotoxins, which are volatile organic compounds that can cause severe problems such as lung infections, liver and kidney disorders, nervous system problems, and even some types of cancer. Trichoderma mold also releases an enzyme that can cause wood to rot. If your home is compromised by Trichoderma mold, it will need professional mold remediation and some areas of your home might require repairs.

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Finding Mold Remediation Services

When you discover a substantial amount of mold (10 square feet or more) or have people with weak immune systems in your household, it’s time to call in the pros. Mold remediation companies advertise online and might bring crews to communities with recent flooding. Professional mold remediation can be expensive, averaging $15 to $30 per square foot, with an average total cost of around $2,300, depending on the extent of the mold problem. Ensure you pay for quality service by checking into their credentials. A remediation contractor should be licensed and bonded and happy to offer a list of past clients as references. In addition, find out if the contractor is certified with a national group, such as the Institute of Inspection Cleaning and Restoration Certification.