What is mold?

Molds are fungi that can grow and prosper in warm, damp environments. They spread and multiply through their spores, and there are thousands of varieties. The most common household molds include:

• Cladosporium

• Penicilliummold

• Alternaria

• Aspergillus

Where does mold grow?

Mold spores are everywhere – both indoors and outdoors, in the air and on many surfaces. Mold spores can enter your home through open doorways, windows, vents, heating, and air conditioning systems or attach to clothing, shoes, bags, and pets.

Where there is moisture, mold will grow: around leaks in roofs, windows, and pipes, or where there has been flooding. Mold grows well on paper products, cardboard, ceiling tiles, wood products, and can also grow in dust, paints, wallpaper, insulation, drywall, carpet, fabric and upholstery.

How does mold affect health?

Mold affects people differently, as some are more sensitive or allergic than others. Those sensitive to mold may experience nasal stuffiness, eye irritation, wheezing, or skin irritation. More severe reactions include fever and shortness of breath, and those with chronic lung illnesses may develop mold infections in their lungs. Mold exposure has also been linked to upper respiratory tract symptoms in otherwise healthy people.

How can people decrease mold exposure?

Sensitive individuals should avoid areas that are likely to have mold, such as compost piles, cut grass, and wooded areas. Inside homes, mold growth can be slowed by controlling humidity levels and ventilating showers and cooking areas. If there is mold growth in your home, you should clean up the mold and fix the water problem. Mold growth can be removed from hard surfaces with commercial products, soap and water, or a bleach solution of no more than 1 cup of bleach in 1 gallon of water.


If you choose to use bleach to clean up mold:

  • Never mix bleach with ammonia or other household cleaners. Mixing bleach with ammonia or other cleaning products will produce dangerous, toxic fumes.
  • Open windows and doors to provide fresh air.
  • Wear non-porous gloves and protective eye wear.

If the area to be cleaned is more than 10 square feet, consult the U.S. Environmental Protection Agency (EPA) guide titled Mold Remediation in Schools and Commercial Buildings. Although focused on schools and commercial buildings, this document also applies to other building types. You can get it by going to the EPA web site at

Always follow the manufacturer’s instructions when using bleach or any other cleaning product.

(Reprinted from the CDC:


Specific Recommendations

  • Keep humidity levels as low as you can—no higher than 50%–all day long. An air conditioner or dehumidifier will help you keep the level low. Bear in mind that humidity levels change over the course of a day with changes in the moisture in the air and the air temperature, so you will need to check the humidity levels more than once a day.
  • Use an air conditioner or a dehumidifier during humid months.
  • Be sure the home has adequate ventilation, including exhaust fans.
  • Add mold inhibitors to paints before application.
  • Clean bathrooms with mold killing products.
  • Do not carpet bathrooms and basements.
  • Remove or replace previously soaked carpets and upholstery.

(Reprinted from the CDC:


Mold Inspections & Removal

For information on mold inspection and removal please refer to the yellow pages.


More Information

For more information of this and other issues, check out our list of Educational Brochures.

If you have any questions please contact us at:

 Environmental Health Services

215 West Mendenhall, Rm 108, Bozeman

(406) 582-3120