Office of Radiation and Indoor Air (6609J)
Office of Research and Development (MD-56)
February, 1991
Introduction
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.
Can I Use Tap Water in My Ultrasonic
or Impeller Humidifier?
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:
1. Use bottled water labeled "distilled." While distilled
water still contains some mineral content, it will likely contain
lower mineral content than most tap water. Distillation is the most
effective method for removing minerals from water.
2. Two additional demineralization processes, deionization
and reverse osmosis, remove most of the minerals from water, but
are generally less effective than distillation. Water demineralized
by these two processes would, on the average, be expected to contain
a higher mineral content than distilled waters. "Purified"
water may be produced by any of these three or other similar processes.
3. Be aware, however, that not all bottled water is
produced using demineralization processes. Bottled waters labeled
"spring", "artesian" or "mineral"
have not been treated to remove mineral content.
4. Consider using demineralization cartridges, cassettes,
or filters if supplied or recommended for use with your humidifier.
5. Be aware, however, that the ability of these devices
to remove minerals may vary widely. Further research is needed to
determine how well, and how long, these devices work. Watch for
the appearance of "white dust," which would indicate that
minerals are not being removed.
6. Also, in areas of the country where the mineral
content in the tap water is high, using distilled water may be less
expensive than cartridges, cassettes, or filters.
Types of Humidifiers and Associated
Pollutants
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:
- Ultrasonic, which create a cool mist by means
of ultrasonic sound vibrations.
- Impeller, or "cool mist," which produce
a cool mist by means of a high speed rotating disk.
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:
- Evaporative, which transmit moisture into the air
invisibly by using a fan to blow air through a moistened absorbent
material, such as a belt, wick, or filter.
- Steam vaporizer, which create steam by heating
water with an electrical heating element or electrodes. "Warm
mist" humidifiers are a type of steam vaporizer humidifier
in which the steam is cooled before exiting the machine.
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.
Recommendations for Use and Care
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.
- Empty the tank, wipe all surfaces dry, and refill
the water in portable humidifiers daily to reduce any growth of
microorganisms; follow the manufacturer's instructions for changing
water in console humidifiers. Be sure you unplug the unit from
the electrical socket first.
- Use water with low mineral content to prevent the
build-up of scale and the dispersal of minerals into the air.
See the box on the left for information on using water with low
mineral content.
- Clean portable humidifiers every third day. Empty
the tank and use a brush or other scrubber to clean it. Remove
any scale, deposits, or film that has formed on the sides of the
tank or on interior surfaces, and wipe all surfaces dry. Again,
be sure you unplug the unit.
- Follow the manufacturer's suggestions on the use
of cleaning products or disinfectants. In the absence of specific
recommendations, clean all surfaces coming in contact with water
with a 3% solution of hydrogen peroxide. If you use any cleaning
or disinfecting agent, rinse the tank thoroughly with several
changes of tap water to prevent dispersal of chemicals into the
air during use.
- Follow the manufacturer's directions on cleaning
and maintaining console and central (furnace mounted) humidifiers.
In particular, if the humidifier contains a tank, do not allow
water to stand in the tank for extended periods of time, and keep
the water clean.
- Keep steam vaporizer humidifiers out of the reach
of children. Steam and boiling water may cause burns.
- Do not humidify to indoor relative humidity levels
exceeding 50 percent. Higher humidity levels may encourage the
growth of biological organisms in the home. Hygrometers, available
at local hardware stores, may be used to measure humidity levels.
Some humidifiers contain a built-in humidistat which may be adjusted
to the proper moisture level. If water condenses on windows, walls,
or pictures, either relocate the humidifier, lower its humidistat
setting, or reduce its use.
- Do not permit the area around the humidifier to
become damp or wet. If dampness occurs, turn the output volume
of the humidifier down. If the humidifier output volume cannot
be turned down, use the, humidifier intermittently. Do not allow
absorbent materials, such as carpeting, drapes, or table cloths,
to become damp.
- Follow the manufacturer's instructions regarding
the use, maintenance, and replacement of any materials supplied
with the humidifier. Use appropriate materials as recommended
by the product manufacturer.
- Clean the humidifier, as directed, at the end of
the humidifying season or when the product will not be in frequent
use. Before storage, make sure all the parts are dry. Dispose
of all used demineralization cartridges, cassettes, or filters.
Store the unit in a dry location. After storage, clean the unit
again and remove any dust on the outside.
Stop using your humidifier and contact your physician
if you have respiratory symptoms which you believe are associated
with periods of use of your home humidifier, even if you are following
maintenance directions.
First Published: March 2002
Updated: April 2007
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