Mold - Basic Information

The following basic information is about mold, and the potential health and remediation issues involved with it.

What is mold, and how common is it?

Molds are everywhere and have existed for millions of years.  Molds are fungal organisms that are essential for the breakdown of dead plant and animal matter.  Molds come in a variety of colors including white, brown, green and black.  Molds reproduce by developing microscopic particles called spores.  Spores are not visible to the naked eye, and are easily carried through the air.  When spores land in a moist environment with an adequate food source, mold begins to grow.

Why should I be concerned about molds? Can molds cause a serious health threat to humans?

Ease of growth - Most molds grow naturally outdoors.  Molds can be easily brought into buildings through open windows and doors, ventilation and air conditioning systems, as well as on pets, clothing, or shoes.  Once indoors, molds grow very easily, only needing moisture and a food source. (Damp paper products, lint, ceiling tiles, drywall, wallpaper, insulation, carpeting, fabric, upholstery and wood can all serve as good nutrient sources for mold growth.)

Health effects - People who suffer from allergies may be more sensitive to mold in the air.  Other susceptible populations may include asthmatics, children and infants, the elderly, or individuals with existing respiratory conditions or a weakened immune system (for example, those undergoing chemotherapy or who have HIV/AIDS).  Symptoms of mold sensitivity are non-specific and may include nasal stuffiness, eye irritation, shortness of breath, wheezing, and in rare cases, mold infections in the lung.

What about "Toxic Mold"?

To date, no scientific evidence exists to positively link residential exposure to mold with specific toxic effects.  The majority of human exposures to mold toxins have occurred from ingesting moldy food.  Some occupations, such as farming and working in greenhouses, where high levels of mold can be encountered, present an inhalation exposure risk for workers.

How can I minimize my exposure, and that of my family, to molds?

Given a source of moisture, mold can grow just about anywhere.  Moisture control and air filtration are necessary to control mold growth.  

There is no way to eliminate all molds from your home, but here are some steps you can take to reduce the opportunities for mold growth:

  • Usually when mold growth is found, it is related to a moisture or water problem.  The source of moisture must be addressed as well as cleanup of the mold growth.
  • After any flooding incident, make sure to completely dry out any affected areas of the house.
  • Do not rely on evaporation alone to adequately dry an area that's been flooded.  Providing good air circulation and using dehumidifiers are important for fast, adequate drying.
  • Carpets that cannot be dried in 48 hours should be removed and discarded.  In general, carpets that have been contaminated with flood or sewer water should be replaced.
  • Repair cracks in basement walls.  Moisture can seep in, creating a moist environment conducive to mold growth.
  • A dehumidifier and/or air conditioner should be used to reduce indoor moisture levels during humid times of the year.
  • Always clean up spills and fix leaks in plumbing promptly and thoroughly.  Mold growth can begin within 24 to 48 hours after a water leak.
  • Regularly clean and empty the drip pans in your air conditioner, refrigerator, and dehumidifier.
  • Typically, it is not necessary to use humidifiers in homes.  Normal activities such as cooking, showering and breathing add adequate moisture to the air.
  • If you have a rental property, consider including a provision in the tenant's lease requiring the prompt reporting of any leaks, floods, or mold growth.  If you are renting, promptly report any leaks, flooding, or mold growth.
  • Be sure the home has adequate ventilation, including exhaust fans in the kitchen and bathrooms.  Let exhaust fans run during, and 20 minutes after, bathing or showering.  Consider installing exhaust fans with humidistat controls.  When the moisture is adequately ventilated from the area, the fan will shut off automatically.
  • Use mold inhibitors, which can be added to paints.  Be sure and read the application instructions carefully.  If not used according to instructions, mold inhibitors can cause health problems for some individuals.
  • Do not carpet bathrooms.

How can I tell if it is mold causing me to feel sick, or some other indoor air problem in my home?

There are other indoor air contaminants that can occur in a home, causing health problems similar to mold exposure.  Exposure to tobacco smoke, pet allergens,  carbon monoxide from faulty furnaces and hot water heaters, and poor sanitation can all cause health problems for residents.  If you are experiencing adverse health symptoms, it is important that you see your physician for a proper evaluation and diagnosis.  Your physician may refer you to a specialist, such as an allergist, for additional tests.  If you seem to feel better when you are away from your home for several hours, this may be an indication that there is a contaminant in your home.  If you and your physician suspect an indoor air quality issue is causing your symptoms, and you are unable to identify and clean up the source of the contamination, call your local health department for more information or for help on where to turn next.  They can either help you directly or refer you to an indoor air quality specialist.

How do I know if I have a mold problem?

If you can see mold growth and/or smell a musty odor, you have a mold problem.  However, it is recommended that you do a thorough inspection to determine the source of the mold growth.

What do I do if I have mold?

Testing - If you can see or smell a mold problem, testing or sampling is typically not necessary.  It is more important to identify and remediate the moisture source and clean up the mold, than to spend the time and money on testing.  In addition, there are no agreed-upon, health-based standards for human exposure to mold or mold spores.  Testing is only indicated in rare instances and should be discussed with an indoor air quality specialist.

Cleanup - Small areas of mold growth on nonporous surfaces can usually be cleaned by the removal of the gross mold buildup, followed by application of a simple bleach solution.  The affected area(s) should be allowed to dry thoroughly (fact sheet detailing the steps involved in mold cleanup).  Extensive cleanup of large areas may require the use of a mold/water cleanup service and the removal of mold-contaminated surfaces (including drywall, carpeting, or wood flooring).

Seeking professional help - If you suspect you have an indoor air quality problem, contact your local health department.  Health department staff may be able to do an in-home inspection, or can refer you to an indoor air quality specialist.  The DHS has established guidelines for inspectors and contractors involved in mold detection and remediation efforts.  For more information, visit Tips on selecting an IAQ consultant or mold contractor.

Complaints - If you have a complaint about the quality of work or other contractor issues, contact the Department of Agriculture, Trade and Consumer Protection at 1-800-422-7128. 


For more information, contact your local health department, or call the Wisconsin Division of Public Health, Bureau of Environmental and Occupational Health, at 608-266-1120.

Last Revised: June 25, 2015