Moisture and biologicals (like molds, mildew, and dust mites). Sources include excessive humidity levels, poorly-maintained humidifiers and air-conditioners, inadequate ventilation, and animal dander.
Check out the Bugs, Mold, and Rot or Home IAQ Overview Instructional Modules from our Training Manual for more information, or read some Q&A below.

Molds, excessive moisture and other biological organisms can cause many undesirable health effects. To protect yourself and your family, read on.

Q: What are some of the health effects?
A: Allergic reactions are the most common health problems associated with biological pollutants. Symptoms often include watery eyes, runny nose and sneezing, nasal congestion, itching, coughing, wheezing and difficulty breathing, headache, dizziness and fatigue. Dust mites have been identified as the single most important trigger for asthma attacks. 

Q: How are biological contaminants transported through the house?
A: Molds and dust mites thrive in areas of high humidity. Mold grows on organic materials such as paper, textiles, grease, dirt and soap scum. Mold spores float throughout the house, forming new colonies where they land. Dust mites thrive on dead human skin cells and in textiles such as bedding, carpeting and upholstery. When these textiles are disturbed during vacuuming, making beds or walking on carpet, the dust particles become airborne. Pollen, plant material that enters through windows or on pets, and animal dander also become airborne when disturbed. Infectious diseases caused by bacteria and viruses are generally passed from person to person through physical contact, but some circulate through indoor ventilation systems. 

Q: If I'm concerned about the biological contaminants in my home, what can I do to deal with the problem?
A: There are no practical tests for biological contaminants for use by non-professionals. However there are signs to watch for. You can sometimes see and smell mold colonies growing on surfaces. Mold growth should be suspected wherever there are water stains, standing water or moist surfaces. 

• Prevent mold growth by keeping basements, bathrooms and other rooms clean and dry. Use a disinfectant to clean surfaces that have mold on them. If carpeting or furnishings become wet, they must be quickly and thoroughly dried or discarded. 
• Humidifiers, dehumidifiers and air conditioning condensing units should be regularly cleaned with a disinfectant such as chlorine bleach. 
• Keep humidity at acceptable levels (less than 50 percent) and make sure there's plenty of ventilation, especially in areas where moisture tends to build up.
• People who are sensitive to dust mites may need to replace carpeting in their homes with hard surfaced flooring and use area rugs that can be removed and cleaned. 
• Vacuums with high efficiency filters or central vacuum systems can help reduce the airborne dust generated by vacuuming.