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Mold

Updated Jun 30, 2022
Stachybotrys chartarum + other species
 
1

Make a Positive Identification

Species: Black Mold
Mold hyphae with blotched pattern

Fevziie Ryman, iStock

Black mold (Stachybotrys chartarum) is often dark colored. It forms webs of filaments (hyphae) that grow on surfaces. They form blotchy patterns. When black mold grows indoors, it can harm your health and damage structures.

Species: Black Mold
Black mold in shower

Black mold grows in high-humidity, poorly ventilated spaces such as bathrooms, kitchens, and laundry rooms. The photo shows a poorly ventilated bathroom with mold on shower tiles.

Species: Black Mold
Black mold growing under sink

MartinFredy, iStock

Black mold grows where there is water damage such as shown in the photo. It grows on a range of materials, including drywall, wood, paper, carpet, painted walls, and cardboard.

Species: Black Mold from Water Damage
Severe water damage

"Black Mold" by satemkemet is marked with CC BY-SA 2.0 (cropped).

Severe water damage due to flooding or fire suppression often supports extensive black-mold growth. It requires repair before the home is safe for habitation. Seek professional help for severe water and mold damage.

Species: Other Molds
Several species of mold growing on bread

Vincent van Zeijst, CC BY-SA 4.0, via Wikimedia Commons (cropped)

Other types of mold contribute to food spoilage. Examples include Cladosporium, Penicillium, and Aspergillus. These food-spoiling molds also grow on moist surfaces in structures.

Species: Fuzzy Mold
Fuzzy mold growing on windowsill

Ftwitty, iStock

The food-spoiling molds often grow as a powdery or fuzzy coating on surfaces. The photo shows a fuzzy mold growing on a window sill. These molds harm your health when they grow on indoor surfaces.

LOOK-ALIKES: ALGAE, MOSS & LICHENS
Species: Algae
Algae growing on vinyl siding

Ftwitty, iStock

Algae grows outdoors on moist surfaces such as vinyl siding and wooden decks. It grows in shady locations such as the north side of buildings.


Different risks or methods

Use a scrub brush and soapy water to get rid of algae as needed. Pressure wash as needed.

Species: Moss
Moss growing in asphalt shingle seam

"Free Insulation" by Luke-Milliron is marked with CC BY-NC-ND 2.0 (cropped)

Moss grows outdoors. It doesn’t cause negative health impacts. Moss becomes a problem when it grows on roofs, patios, and walkways.


Different risks or methods

Remove moss by scraping and scrubbing.

Species: Lichens
Lichen on rock surface

"Lichen close-up" by Linda, Fortuna future is marked with CC BY-NC 2.0 (cropped)

Lichen grows outdoors. Its growth doesn’t cause negative health impacts. Lichen generally doesn’t require management.


Helpful

Lichens are usually not a problem and can be left alone.

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2

Mold Benefits

  • Molds are important in the natural world. They are fungi that break down organic materials such as wood.
  • When molds grow outdoors, they are not a problem.
 

Mold Risks

  • Molds growing indoors are a problem and require action.
  • Indoor mold growth has a negative impact on indoor air quality and human health.
  • Mold exposure can cause a stuffy nose, sore throat, coughing, or skin rash. People who have asthma or are immune-compromised may have severe reactions to mold.
  • Unchecked mold growth damages structures and stains surfaces. Mold damage requires repair.
Don’t let mold grow in your home or structures you care about. Mold is a human health hazard. It damages structures.
Risk Card
Does it cause harm?
Adults & Children
High
Property
High
Pets
High
Annoyance
High
Environment
None
Action Highly Recommended
 
3

TAKE ACTION

If mold is growing in your home, you need to remove the mold and fix the moisture problem.

Do I need to take action?
Yes. If you find mold in your home, clean it up right away. Take action to reduce moisture and increase ventilation where you found mold growth.

What if I do nothing?

  • Mold affects human health. Reactions to mold are common in people and pets. Mold exposure irritates eyes, skin, nose, throat, and lungs of both mold-allergic and non-allergic people. Molds can trigger asthma symptoms in sensitive individuals.
  • Mold can damage your property. Unchecked mold growth damages and stains surfaces in structures. Mold damage requires repair.

Do you need professional help?

If controlling mold in your home seems overwhelming, consider hiring a professional. See How to Hire a Mold Removal Specialist.

NEED HELP?

Consider a licensed pest control company. Learn How to Hire a Pest Control Company.
Your local Extension Specialist in Oregon  and other states  can suggest other methods.

 
4
Solutions for Mold (Indoors)

How mold spores get into structures:

  • Mold spores enter your home on our bodies, pets, and through open doorways, windows, and vents.
  • The spores are circulated by heating and air-conditioning systems.
  • There is no way to prevent spores from entering your home.

Determine the extent of mold damage to various materials in your home:

  • Remove and dispose of moldy carpet, furniture, and cloth. Once they develop mold, porous materials can’t be salvaged. Dispose of them in a landfill.
  • For semi-porous materials such as drywall and wood flooring, determine the extent of the mold damage. If the mold can’t be scrubbed off, the materials should be removed. Or scrub and scrape mold off the material, if it’s cleanable.
  • Mold can be removed from hard (non-porous) hard surfaces such as glass and sealed countertops.

Removing mold:

  • Scrape and scrub mold off cleanable materials.
  • After scraping and scrubbing mold, use disinfectant.
  • Then use fans and dehumidifiers to circulate air. Moving the air will help to dry out an area.
  • See mold-cleaning methods.

Preventing mold:

  • You must fix the moisture problem that supports mold growth.
  • Use preventive measures to keep mold from regrowing.
To control mold growth, you must lower indoor humidity levels. Humidity must be less than 50% all day and throughout the year to prevent mold growth. If you can’t get the humidity below 50%, mold will likely regrow. Improve ventilation by installing a bathroom fan, for example, which helps to lower humidity.

Jump To

Method Does it work? Is it safe? Recommendation
A
Determine Extent of Mold Damage
Effective
Moderate risk
B
Scrape, Scrub & Disinfect, Then Dry
Effective
High risk
Use if Necessary
C
If Using Disinfectant, Protect Yourself & Minimize Risks
D
Prevent Mold
 
A

Determine Extent of Mold Damage

Non-Chemical Method

yavdat,iStock

Determine Extent of Mold Damage

  • Examine the mold damage in your home.
  • Determine damage to porous materials such as carpet, furniture, and clothing.
  • For semi-porous materials such as drywall and wood flooring, determine the extent of the mold damage.
  • Hard (non-porous) surfaces such as glass and metal can be cleaned. See mold-cleaning methods below.
Does it work?
Effective
  • Determining the extent of damage is required for mold control.
  • Use preventive measures to keep mold from regrowing.
How much effort?
High effort

Mold is a human health hazard. All effort to control it is required.

What's the risk?
Moderate risk

Wear an N95 respirator mask (or better) to protect your lungs when cleaning mold.

Possible risk of exposure or harm from chemicals
NONE

Examine materials. Dispose of moldy porous materials and mold-damaged semi-porous materials. Remove drywall as needed. Fix leaks.

Moldy fabric

Laymul, iStock

Dispose of Moldy Carpet, Furniture & Clothing

Remove moldy carpets/padding, upholstered furniture, and bedding from your home. Take the moldy items to the landfill. Porous materials that can’t be salvaged when moldy include:

  • Carpeting
  • Clothing
  • Bedding
  • Pillows
  • Mattresses
  • Upholstered furniture
  • Fabrics
  • Leather
  • Wall Insulation
  • Ceiling tile
Worker peeling back wallpaper to find mold underneath the surface

yavdat,iStock

Determine Extent of Damage for Semi-porous Materials

For semi-porous materials, determine the extent of the mold damage. The photo shows a worker peeling back wallpaper to find mold underneath the surface.

Semi-porous materials include:

  • Wood
  • Drywall
  • Tile grout
  • Hardwood floor
  • Linoleum

If the mold is just on the surface, you can scrape and scrub these semi-porous materials. If the mold can’t be removed, dispose of damaged items in the landfill.

Drywall removed to wooden wall framing

"Stripped Wall" by Pattie is marked with CC BY-NC-ND 2.0 (cropped).

Inspect Drywall, Repair as Needed

  • Inspect drywall for water and mold damage. Determine whether you can clean it or mold has impregnated the drywall.
  • Remove all the damaged drywall to the wooden structure as shown in the photo.
  • Clean the wooden structure with bleach or cleaner.
  • Dry the area with a fan.
Water damage and mold from leaking plumbing

MartinFredy, iStock

Fix Moisture Problems & Water Damage

  • Remove sources of moisture. Fix leaky roofs, windows, faucets, and pipes.
  • To fix the leaky faucet, water damage, and mold damage shown in the photo requires plumbing and carpentry skills.
 
B

Scrape, Scrub & Disinfect, Then Dry

Chemical Method: Use with caution

Mitt, iStock

Scrape, Scrub & Disinfect, Then Dry

Use if Necessary
  • Scrape and scrub off of cleanable surfaces.
  • Use disinfectant.
  • Dry the area with a fan.
Does it work?
Effective

You must Use preventive measures to keep mold from regrowing.

How much effort?
High effort

Scraping and scrubbing mold requires significant effort. It is required to control mold.

What's the risk?
High risk
  • Wear an N95 respirator mask (or better) to protect your lungs when cleaning mold.
  • Wear goggles to protect your eyes, and gloves to protect your skin from mold and cleaning products.
  • Disinfectant products such as bleach are registered pesticides.
  • Disinfectants come with real risks. ALWAYS read the entire label front to back. Review instructions even for brands you know.
Possible risk of exposure or harm from chemicals
Using pesticides includes some amount of risk. The lowest risk comes without using pesticides.

You may be exposed to a pesticide if you:

  • Get it on your skin
  • Breathe it in
  • Eat or smoke afterward without washing hands
  • Touch or eat plants that are wet with spray (you, pets, or children)
  • Bring it inside on your shoes or clothes

Follow directions closely to reduce risk.

Remove mold from hard surfaces. Then disinfect it and dry it.

Bleach product and gloves near bathroom sink

Weston Miller, Oregon State University

Scrape and Scrub Mold from Hard Surfaces and Disinfect

  • Scrape and scrub mold off hard (non-porous) surfaces. Use cleaning products specifically offered for mold.
  • Or use soap and water followed by a bleach solution (No more than 1 cup of household bleach in 1 gallon of water).

You can clean mold off of non-porous materials such as:

  • Some tiles
  • Some sealed countertops
  • Glass
  • Metal
High-volume fan for surfaces after mold removal

VisualCommunications, iStock

After Cleaning, Thoroughly Dry the Area

  • After you remove mold from an area and then use disinfectant, dry the area with a fan.
  • High-volume fans (air movers) such as the one shown in the photo are available at rental centers.
 

If Using Disinfectant, Protect Yourself & Minimize Risks

Chemical Method: Use with Caution
Worker wearing respirator and protective suit and gloves cleaning mold

amixstudio, iStock

Wear a Respirator, Eye Protection & Gloves

  • Wear an N95 respirator mask (or better) to protect your lungs when cleaning mold.
  • Wear goggles to protect your eyes, and gloves to protect your skin from mold and cleaning products.

Why is it Important to Read Disinfectant Labels?

  • They have detailed information on how to use the product correctly and legally.
  • They contain information on potential hazards of the product.
  • They offer instructions you should follow for poisonings and spills.

READ THE LABEL & Follow Instructions
It has instructions to protect you and the environment.

  • Household disinfectants are registered pesticides.
  • Labels describe the areas that can be treated. For example hard, non-porous surfaces include glass, metal, and most countertops. Wood and linoleum may absorb the product.
  • Sometimes the surface needs to remain wet with disinfectant for a period of time in order to work. Check the label for “contact time” or “dwell time.”
  • Use a magnifying glass.
  • Pay attention to CAUTION, WARNING, and DANGER statements.
  • Pay attention to the PRECAUTIONARY STATEMENTS.
  • The law states you must read and follow disinfectant instructions.

Protect Yourself
Eye, skin & lung irritants

  • Wear an N95 respirator (or better), gloves, safety glasses, a long-sleeve shirt, pants, socks, and shoes.
  • Avoid contact with eyes, skin, or clothing.
  • Never mix bleach with ammonia. When combined, these two common household cleaners release a toxic gas. Exposure can cause eye and throat irritation. High concentrations can lead to coma or death.

Storage & Disposal

  • Store in a secure storage area away from children.
  • Don’t put unused disinfectant products in the trash. Take them to a hazardous waste facility.
  • Never pour product down any drain or waterway.

Call  1-800-CLEANUP (1-800-253-2687) to find out where to dispose of disinfectants.

For the Portland metro region in Oregon, contact Metro’s Recycling Information. Call  503-234-3000, email   or visit Metro’s website  

More about:

About Using Pesticides on School Grounds in Oregon

If using pesticides on school grounds, there are special rules in Oregon. See School Integrated Pest Management  (Oregon Department of Agriculture).

NEED HELP?

The National Pesticide Information Center (NPIC)  can answer questions about pest control chemicals.
 1-800-858-7378 or npic@ace.orst.edu  

Consider using a licensed pest or weed control company. Learn How to Hire a Pest Control Company.

Your local Extension Specialist in Oregon  and other states  can suggest other methods.

 

Prevent Mold

Ceiling fan in bathroom

Yanggiri, iStock

Improve Ventilation & Air Circulation / Filtration
  • Ventilate shower, laundry, and cooking areas.
  • Install a ventilation fan to vent humid areas of your home.
  • Clean the fan blades periodically to keep mold from growing in the fan itself.
Worker cleaning air duct

Flowingking, CC BY-SA 4.0, via Wikimedia Commons (cropped)

Clean Air Duct Surfaces
  • As part of your home maintenance plan, include professional air duct cleaning services.
  • They remove dust, debris, and mold from air ducts.
  • Mold spores enter your home’s air duct system. Mold can grow in the ducts when there is enough moisture.
Mold on window pane

zeleno, iStock

Monitoring and Ongoing Efforts
  • Look for mold where you have previously removed it. Clean it as needed.
  • Fix moisture problems. Seek professional help if needed.
  • Improve ventilation and air circulation / filtration.
  • Unless the moisture problem has been fixed, mold will probably grow again.
 

HEALTH & SAFETY TIP

Never mix bleach with ammonia. When combined, these two common household cleaners release a toxic gas. Exposure can cause eye and throat irritation. High concentrations can lead to coma or death.

Photo of vapor with lightig

yudhistirama, iStock


Content provided by editor Weston Miller and writers J. Jeremiah Mann and Kaci Buhl.

 Peer reviewed by OSU Department of Horticulture.

Photo of Weston Miller

Weston Miller

Community and Urban Horticulturist

Since 2007, Weston Miller has served as Community and Urban Horticulture faculty for Oregon State University Extension Service for Clackamas, Multnomah, and Washington Counties. He manage the popular Master Gardener program. We train and manage volunteers to answer the public’s gardening and pest management questions.

J. Jeremiah Mann

J. Jeremiah Mann

J. Jeremiah Mann completed a Physical Science undergraduate degree at Humboldt State University, and M.S, Ph.D focusing on plant science topics at UC Davis. He went on to work for the Natural Resources Conservation Service and in a leadership position serving a private agricultural technology company. He currently lives in Sacramento California where he consults on pest and property management topics.

Photo of Kaci Buhl

Kaci Buhl

At the state level, I lead the Pesticide Safety Education Program (PSEP). The program hosts live recertification events around the state, serving over 1,000 licensed pesticide applicators each year. We also produce web-based training modules and license-preparation study manuals. Special training for unlicensed pesticide applicators is also available through a grant from the USDA Specialty Crop Block Grant Program. The PSEP at OSU works closely with the Oregon Department of Agriculture's Pesticides Division.

MOLD REFERENCES

Mold  
US Environmental Protection Agency

Facts about Stachybotrys chartarum  
Centers for Disease Control and Prevention

Mold  
Centers for Disease Control and Prevention

Moisture Control and Mold  
National Pesticide Information Center