Humidifiers are commonly used in homes to relieve the physical discomforts of dry nose, throat, lips, and skin. The moisture they add to dry air also helps alleviate common nuisances brought on by winter heating, such as static electricity, peeling wallpaper, and cracks in paint and furniture. However, excess moisture can encourage the growth of biological organisms in the home. These organisms include dust mites, which are microscopic animals that produce materials causing allergic reactions to household dust, and molds.
Recent studies by the Environmental Protection Agency (EPA) and the Consumer Product Safety Commission (CPSC) have shown that ultrasonic and impeller (or "cool mist") humidifiers can disperse materials, such as microorganisms and minerals, from their water tanks into indoor air. At present, only limited information is available on the growth of microorganisms and the dispersal of microorganisms and minerals by home humidifiers. Proper care and cleaning of ultrasonic and impeller humidifiers are important for reducing potential exposures to microorganisms, such as bacteria and molds. Microorganisms often grow in humidifiers which are equipped with tanks containing standing water. Breathing mist containing these pollutants has been implicated as causing a certain type of inflammation of the lungs.
The Federal government has not concluded that the dispersal of minerals by home humidifiers poses a serious health risk. Nevertheless, using water with lower mineral content will reduce exposures to these materials.
The young, the elderly, and those people with lung diseases or respiratory allergies may be particularly susceptible to certain types of airborne pollutants. However, if you follow the recommendations for the use and care of home humidifiers provided in this fact sheet, the potential for dispersal of microorganisms and minerals from your humidifier should be reduced.
Console humidifiers are encased in cabinets which are designed for floor use. Portable humidifiers are smaller and more readily moved. Central humidifiers are built into heating and air-conditioning systems, and humidify the whole house.
The two types of humidifiers which generally appear to produce the greatest dispersions of both microorganisms and minerals are:
Two additional types of humidifiers can allow for growth of micro-organisms if they are equipped with a tank that holds standing water, but generally disperse less, if any, of these pollutants into the air. These are:
Note: Steam vaporizer and evaporative humidifiers are not expected to disperse substantial amounts of minerals. A steam vaporizer tested by EPA did not disperse measurable amounts of minerals; evaporative humidifiers have not been tested by EPA for mineral dispersal.
The Federal government has not concluded that using tap water in ultrasonic or impeller humidifiers poses a serious health risk. However, researchers have documented that these humidifiers are very efficient at dispersing minerals in tap water into the air. In addition, some consumers are bothered by a "white dust" that may appear on surfaces during use of these devices. Most importantly, minerals in tap water may increase the development of crusty deposits, or scale, in humidifiers. Scale can be a breeding ground for microorganisms.
Retarding the growth of scale is the most compelling reason to find alternatives to tap water. For this reason, or if white dust is a problem or you wish to minimize your exposure to minerals in the tap water as a matter of prudence, you should either:
It is important to use a humidifier only when conditions require it, to use the correct moisture setting for existing conditions, and to clean it thoroughly.
The possible health effects resulting from the dispersal of microorganisms and minerals by home humidifiers are not fully understood. Meanwhile, it may be prudent to reduce the potential for personal exposures to these materials by taking the following precautions, particularly when using ultrasonic and impeller humidifiers.