Molds are part of the fungi kingdom, which includes yeasts, molds, smuts and mushrooms. Molds are ubiquitous—many thousands of mold species can be found indoors and outdoors throughout the year.

Mold can grow almost anywhere, as long as optimal temperatures, moisture, oxygen, and food sources, such as organic matter are present. Optimal temperatures for mold growth vary from species to species. Most molds tend to favor warmer temperatures; however, many molds can grow in a variety of temperatures, so long as there is sufficient moisture and oxygen. Viable molds reproduce by spreading spores through the air.

Potential Health Effects

Potential health effects from environmental mold spore exposure vary from person to person. Most persons who do not have mold-related allergies are not affected by typical airborne spores. However, individuals with allergies (sensitivities) to mold or immunodeficiency may have more adverse reactions.

For more information regarding the potential health effects of exposure to environmental molds, please read the American College of Occupational and Environmental Medicine (ACOEM) position statement .


In order to prevent the active growth of mold, moisture sources and indoor relative humidity must be controlled. OSHA recommends the following mold prevention tips:

  1. Repairing plumbing leaks as soon as possible.
  2. Look for condensation and moisture. Fix sources of moisture incursion as soon as possible.
  3. Preventing moisture condensation.
  4. Keeping HVAC drip pans clean, flowing properly, and unobstructed.
  5. Performing regularly scheduled building HVAC inspections and maintenance, including filter changes.
  6. Maintaining indoor relative humidity below 70% (25 – 60%, if possible).
  7. Venting moisture-generating appliances, such as dryers, to the outside where possible.
  8. Venting cooking areas and bathrooms according to local code requirements.
  9. Cleaning and drying wet materials as soon as possible, but not more than 48 hours after discovery.
  10. Providing adequate drainage around buildings and sloping the ground away from building foundations. Follow local building codes.
  11. Pinpointing areas of water infiltration, identifying the cause and taking preventive action to prevent recurrence.


Because of the variation in the effect of mold on individuals, there are currently no government standards regarding the presence or control of indoor mold. However, most experts agree that the prevention of active mold growth is prudent, in order to prevent potential problems.