Mold & Air Quality

Please note that Snohomish County Health Department does not identify or test mold, and does not have an indoor air quality program. The materials provided on this web page are designed to answer basic questions about mold.

Clean up and prevent mold in your home

What are molds?

Molds are a type of fungus. Molds occur widely in nature and outdoors. There is no practical way to get rid of all mold spores indoors.

How do molds grow in my home?

Molds grow in our homes because of too much water. Controlling moisture is the most important thing to remember when dealing with mold. Leaky plumbing or a hole in the roof can let water into your home and help mold grow. Humid air from cooking, breathing or showering can also lead to mold growth unless you let the damp air out and fresh air into your home. Common materials we have in our homes like paper, drywall, leather, and carpeting provide food for mold growth if they get wet. 

Where can I find molds in my home?

You might find mold in water damaged areas, on the inside of cold exterior walls, behind dressers, headboards and in closets where things are stored against a cold outer wall. Other areas where mold often grows are kitchens, bathrooms, laundry or utility rooms, and basements. Carpets and other water-damaged materials will easily support mold growth. Mold may also grow undetected inside wall spaces, under carpet, and inside heating ducts.

How do I know if I have a mold problem?

Testing for molds is usually not necessary in order to solve the problem. If you see or smell mold, or a musty odor, you might have a mold problem. You should clean up the mold as soon as possible. The presence of mold does not necessarily lead to symptoms. 

How can I control or prevent molds from growing in my home?

Mold may show up in the dampest places first: 

  • Stop all water leaks first. 
  • Repair leaky roofs and plumbing right away. 
  • Move water away from basement walls and concrete slabs.

Increase air movement within your home. If needed, use ceiling or standing fans to circulate air throughout your home. Pay special attention to outside walls.

Provide warm air to all rooms of your home: 

  • Leave closet doors slightly open. 
  • Move furniture and large objects away from outside walls. 
  • Leave a few inches for air to move between the wall and belongings. 
  • 'Flush' the air in your home at least once or twice a day. Do this by opening all windows and turning on all exhaust fans for five minutes. Close windows and reheat home to 70 degrees.

Make sure you have working exhaust fans in bathrooms, kitchens and laundry rooms. Run fans while bathing, cooking or doing laundry and for at least 30 minutes afterwards.

If your living area is constantly humid even with proper ventilation and temperature control, you may want to consider the use of a dehumidifier. Dehumidifiers can be helpful to control moisture in basements or daylight basements.

Ventilate and insulate attic and crawl spaces. Cover dirt in the crawl space with heavy plastic.

Clean and dry water damaged carpets, clothing, bedding and fabric furniture within 24 to 48 hours. Otherwise consider throwing it away and replacing with new. Vacuum (with a HEPA vacuum if possible) and clean your home regularly.

How do I clean up mold in my home?

If you see or smell mold, it's time to clean up.

Try to determine how much of an area has a mold problem. For a larger area (greater than 10 feet square) you need to pay attention to personal protection. Use goggles, gloves and breathing protection, such as an N95 dust mask.

Isolate the work area as much as possible. Cover heat vents. Close the door or hang plastic across open doorways and seal with tape. Open a window or use an exhaust fan.

Cover all furniture in the area. Sheets or paint drop clothes can be used. For a large area of mold, move all belongings to another place before clean up. Sort articles for later clean up. See below for cleaning household articles.

Remove severely mold-damaged materials by putting them in bags and throwing away.

Thoroughly dry the area. It is not necessary to use bleach. You can’t get enough bleach to penetrate and kill the mold before the bleach evaporates, and bleach is irritating to your skin and lungs. Scrub the area with a mix of dishwashing liquid and water or liquid laundry detergent (no bleach) and water. Use just enough detergent to make the water a little sudsy. 

Give the entire area a good cleaning. Vacuum floors and wash bedding and clothes if needed. Consider hiring a professional if the area is larger than 10 square feet, or roughly the size of a full sheet of newspaper.

Belongings should be sorted into three categories:

  • Permeable and washable: Clothing, bedding and other washable items should be run through the laundry. 
  • Non-permeable and washable: wood, metal, plastic, glass and ceramics. First try scrubbing clean with a liquid soap. If that does not work, use one cap of bleach to one quart of water. Spot test to check for spotting from the bleach. Wipe down items, let sit for 20 minutes and then dry. 
  • Permeable but not washable: Beds and furniture fit into this category. If items such as mattresses or couches are moldy, you should consider disposal and replacement. If not take them outside; give them a good vacuuming and let them air out. If you do not see or smell mold on the items after this, they should be okay.

Watch for any new mold growth or health effects. Carpeting and upholstered furniture, if not too badly damaged by mold, can sometimes be cleaned by a professional using hot-water extraction or steam-cleaning. Rental rug-shampooing units are usually ineffective for proper removal of mold and in some cases may cause more mold to grow.

How am I exposed to molds and what are the health effects?

We are exposed to mold by breathing mold spores from the air. When mold is disturbed, levels of spores in the air increase, making it important to wear protective equipment for cleanup. Eating mold-contaminated foods or material may also expose us.

There may be toxic effects or allergy. Molds sometimes produce toxins.

Health effects from toxic exposure may include:

  • Tiredness
  • Nausea
  • Headache
  • Respiratory or eye irritation

Allergic reaction to mold may include:

  • Eye, nose, and sinus irritation
  • A skin rash
  • Problems with asthma

Allergies may be to a specific mold species and you may not react to all mold species. Persons most at risk include young children, elderly, those with compromised immune systems and people with respiratory conditions such as asthma.


Mold information

Mold—Washington Department of Health.

A Brief Guide to Mold, Moisture, and Your Home (EPA)—Includes tips on hiring a professional.

Northwest Clean Air Agency—Videos and brochures providing education, tips and guidance.

Tenant and landlord information

Washington Residential Landlord Tenant Act—defines the minimum duties of landlords and tenants of residential dwellings.

Volunteers of America—The dispute resolution center provides a wide range of professional and affordable conflict resolution services that include Fair Housing and Landlord/Tenant Services