Mold 101: Introduction and Prevention

February 26, 2018

What is mold?

Molds are various types of fungi (singular – fungus) that grow in filaments and reproduce by forming spores that can travel through the air. The term mildew is sometimes used to refer to some kinds of mold, particularly mold in the home with a white or greyish color.

Health effects

Molds produce irritating substances that may act as allergy causing substances (allergens) in sensitive individuals. Some molds produce toxic substances known as mycotoxins but mold itself is not poisonous or toxic. The term “toxic mold,” therefore, refers to the fact that certain kinds of mold can produce mycotoxins.

Allergic reactions to mold are the most common health effects of mold and are therefore the greatest health risk related. Allergic reactions may happen immediately or develop after a period following exposure. Both growing mold and mold spores may lead to allergic reactions. Symptoms and signs of mold allergy may include:

  • sneezing
  • runny nose
  • coughing
  • wheezing
  • watery eyes
  • redness of the eyes
  • itchy eyes
  • skin irritation or rash

People with mold allergies may have more severe reactions, such as asthma attacks.


Mold spores are literally everywhere and can be found in essentially any environment or season. Sources within homes, businesses, and schools include leaks through roofs, walls, and basements; condensation on windows and in bathrooms; standing water in drains, on floors, and in heating, cooling, and dehumidifying equipment; heating/cooling ducts; and wet floors and carpets.

Homes and structures often provide many opportunities for mold spores to grow, even in the absence of open water leaks: seepage through foundation walls and cellar floors, dehumidifiers and air conditioners, window condensation, defective plumbing, damp bathrooms, air filters, and potted plants.

There are no EPA or government standards that have been established for mold or mold spore levels in residential or commercial areas, so it is impossible to prove that a building or room complies with any health regulations concerning mold exposure.

Common indoor mold species include Aspergillus, Alternaria, Acremonium, Cladosporum, Dreschslera, Epicoccum, Penicillium, Stachybotrys, and Trichoderma (Storey).

Preventing and eliminating indoor mold

Mold growth in homes, schools, and businesses should be eliminated for the sake of human health, structural integrity, and quality of life.

Controlling moisture is the key to preventing mold growth. This requires stopping leaks, removing standing water, venting areas prone to condensation (especially bathrooms and kitchens), and immediately drying or removing damp carpets and furniture. Mold-inhibiting paints can be used indoors, and air conditioners and dehumidifiers can be used in humid weather (U.S. Centers for Disease Control and Prevention).

Small amounts of mold on hard surfaces can be removed with commercial mold and mildew removers, or with a solution of bleach and water (one cup bleach to one-gallon water) (U.S. Environmental Protection Agency, Mold remediation). Follow product instructions carefully to avoid breathing fumes, irritating skin, or splashing chemicals in the eyes. Large amounts of mold require specialized removal techniques and personal protective equipment.

9 ways to prevent moisture indoors:

  1. Identify problem areas in your home and correct them
  2. Dry wet areas immediately
  3. Prevent moisture with proper ventilation
  4. Equip your home with mold-resistant products
  5. Monitor humidity indoors
  6. Direct water away from your home
  7. Clean or repair roof gutters
  8. Improve air flow in your home
  9. Keep mold off household plants


Storey E, Dangman KH, Schench P, DeBernardo RL, Yang CS, Bracher A, Hodgson MJ. Guidance for clinicians on the recognition and management of health effects related to mold exposure and moisture indoors. Farmington (CT): University of Connecticut Health Centre, Division of Occupational and Environmental Medicine, Centre for Indoor Environments and Health; 2004.

U.S. Centers for Disease Control and Prevention. Basic facts: Molds in the environment. Updated Feb 8 2010. Accessed April 3 2014.

U.S. Environmental Protection Agency. Environmental Relative Moldiness Index (ERMI) Research Tool. Accessed April 3, 2014.

U.S. Environmental Protection Agency. Mold remediation in schools and commercial buildings. Updated June 25 2001. Accessed April 3 2014.