“A number of factors allow biological agents to grow and be released into the air. Especially important is high relative humidity, which encourages house dust mite populations to increase and allows fungal growth on damp surfaces.” -Indoor Air Pollution: An Introduction for Health Professionals
Lack of Humidity Control in a home can lead to mold, mildew, and other biological growth. This in turn can lead to a variety of health effects ranging from more common allergic reactions, to asthma attacks, and hypersensitivity pneumonitits, for example. In addition to health problems, high relative humidity or water that enters building cavities that is not allowed to dry quickly can lead to problems such as rot, structural damage, and premature paint failure. -EPA: Remodeling Your Home? Controlling Moisture
At Healthy Air USA, we know that if the inside environment is to be controlled, then the humidity levels must be maintained as well. This, however, does not mean that more dehumidification is better. The optimum range of relative humidity in an indoor environment is between 40% and 50%. Above 50%, an environment will grow mold and have more problems with dust mites. Below 40%, bacteria will begin to thrive.
Homes with humidity levels above 50% allow mold, dust mites, bacteria and viruses to thrive. High humidity also increases the rate at which VOCs are released into the air. Mold is considered by the EPA to be the “greatest threat to the indoor environment”.
Dust mites are the most common allergen-producing organism found in the home. They are members of the arachnid (spider) family. In order to get water, dust mites must absorb moisture from the air. With humidity levels controlled between 40% and 50%, dust mites can not absorb enough water and die.
Humidity control, though, is only a part of the solution. For a complete solution to indoor air quality, you will need to have good ventilation, air filtration, and protect the building envelope itself.