Mold Basics

Why is mold growing in my home?

Molds are part of the natural environment.  Outdoors, molds play a part in nature by breaking down dead organic matter such as fallen leaves and dead trees, but indoors, mold growth should be avoided.  Molds reproduce by means of tiny spores; the spores are invisible to the naked eye and float through outdoor and indoor air.  Mold may begin growing indoors when mold spores land on surfaces that are wet.  There are many types of mold, and none of them will grow without water or moisture.

Can mold cause health problems?

Molds are usually not a problem indoors, unless mold spores land on a wet or damp spot and begin growing.  Molds have the potential to cause health problems.  Molds produce allergens (substances that can cause allergic reactions), irritants, and in some cases, potentially toxic substances (mycotoxins).  Inhaling or touching mold or mold spores may cause allergic reactions in sensitive individuals.  Allergic responses include hay fever-type symptoms, such as sneezing, runny nose, red eyes, and skin rash (dermatitis).  Allergic reactions to mold are common.  They can be immediate or delayed.  Molds can also cause asthma attacks in people with asthma who are allergic to mold.  In addition, mold exposure can irritate the eyes, skin, nose, throat, and lungs of both mold-allergic and non-allergic people.  Symptoms other than the allergic and irritant types are not commonly reported as a result of inhaling mold.  Research on mold and health effects is ongoing.  This brochure provides a brief overview; it does not describe all potential health effects related to mold exposure.  For more detailed information consult a health professional.  You may also wish to consult your state or local health department.

How do I get rid of mold?

It is impossible to get rid of all mold and mold spores indoors; some mold spores will be found floating through the air and in house dust.  The mold spores will not grow if moisture is not present.  Indoor mold growth can and should be prevented or controlled by controlling moisture indoors.  If there is mold growth in your home, you must clean up the mold and fix the water problem.  If you clean up the mold, but don't fix the water problem, then, most likely, the mold problem will come back.

Moisture and Mold Prevention and Control Tips
 

Moisture Control is the Key to Mold Control

Mold growing on the surface of a unit ventilator.  Click on the image for a larger version.

• When water leaks or spills occur indoors - ACT QUICKLY.  If wet or damp materials or areas are dried 24-48 hours after a leak or spill happens, in most cases mold will not grow.
   
• Clean and repair roof gutters regularly.
   
• Make sure the ground slopes away from the building foundation, so that water does not enter or collect around the foundation.
   
• Keep air conditioning drip pans clean and the drain lines unobstructed and flowing properly.
   
• Keep indoor humidity low.  If possible, keep indoor humidity below 60 percent (ideally between 30 and 50 percent) relative humidity.  Relative humidity can be measured with a moisture or humidity meter, a small, inexpensive ($10-$50) instrument available at many hardware stores.
   
• If you see condensation or moisture collecting on windows, walls or pipes ACT QUICKLY to dry the wet surface and reduce the moisture/water source.  Condensation can be a sign of high humidity.

Actions that will help to reduce humidity
 

Condensation on the inside of a windowpane.

• Vent appliances that produce moisture, such as clothes dryers, stoves, and kerosene heaters to the outside where possible.  (Combustion appliances such as stoves and kerosene heaters produce water vapor and will increase the humidity unless vented to the outside.)
   
• Use air conditioners and/or de-humidifiers when needed.
   
• Run the bathroom fan or open the window when showering.  Use exhaust fans or open windows whenever cooking, running the dishwasher or dishwashing, etc.

Actions that will help prevent condensation
 

Mold growing on a wooden headboard in a room with high humidity.  Click on the image for a larger version.

• Reduce the humidity.
   
• Increase ventilation or air movement by opening doors and/or windows, when practical.  Use fans as needed.
   
• Cover cold surfaces, such as cold water pipes, with insulation.
   
• Increase air temperature.

Testing or Sampling for Mold

Is sampling for mold needed?  In most cases, if visible mold growth is present, sampling is unnecessary.  Since no EPA or other federal limits have been set for mold or mold spores, sampling cannot be used to check a building's compliance with federal mold standards.  Surface sampling may be useful to determine if an area has been adequately cleaned or remediated.  Sampling for mold should be conducted by professionals who have specific experience in designing  mold sampling protocols, sampling methods, and interpreting results.  Sample analysis should follow analytical methods recommended by the American Industrial Hygiene Association (AIHA), the American Conference of Governmental Industrial Hygienists (ACGIH), or other professional organizations.

Rust is an indicator that condensation occurs on this drainpipe.  The pipe should be insulated to prevent condensation.  Click on the image for a larger version.

Renters:  Report all plumbing leaks and moisture problems  immediately to your building owner, manager, or superintendent.  In cases where persistent water problems are not addressed, you may want to contact local, state, or federal health or housing authorities.