Note: A-1 House Inspectors does not perform
environmental inspections. It is our contention that
home inspectors are not properly trained for these
services, although they may advertise to the contrary. We strongly recommend the use
of an Industrial Hygienist to address these concerns.
Mold, dust mites, fungi, spores, and
pollen:
Bioaerosols in the human environment
What are bioaerosols?
A healthy indoor
environment is important to you and your family. This
includes keeping the air free of biological
contaminants, which can cause health problems.
Scientists call these airborne contaminants
bioaerosols.
Bioaerosols are
extremely small living organisms or fragments of living
things suspended in the air. Dust mites, molds, fungi,
spores, pollen, bacteria, viruses, amoebas, fragments of
plant materials, and human and pet dander (skin which
has been shed) are some examples. They cannot be seen
without a magnifying glass or microscope.
Can bioaerosols cause health problems?
They can cause
severe health problems. Some, like viruses and bacteria,
cause infections (like a cold or pneumonia). Others
cause allergies. Both allergic responses and infections
may be serious or even fatal.
An allergic
reaction occurs when a substance provokes formation of
antibodies in a susceptible person. We call substances
which will cause an allergic reaction in some people
antigens or allergens. Bioaerosols may cause
allergic reactions on the skin or in the respiratory
tract. Rashes, hay fever, asthma (tightness in the
chest, difficulty in breathing), and runny noses are
common allergic reactions.
A few people
develop a severe allergic reaction in the lung, which
can destroy lung tissue. This is called
hypersensitivity pneumonitis. It is not an
infection, but repeated episodes can lead to infections
of the lung, such as bacterial pneumonia.
Hypersensitivity
pneumonitis can be triggered by exposure to very small
amounts of the allergen, once a person is sensitive to
it. Symptoms can range from tightness in the chest,
cough, and difficulty in breathing, to low-grade fever,
muscle aches, and headaches.
What are sources of bioaerosols in the home?
Molds, mildews,
bacteria, and dust mites like the same conditions that
we do--warmth and moderate to high humidity. They need
little more than a constant moisture supply for
survival. You may find bacteria, molds, and mildews in
air conditioning equipment, humidifier reservoirs,
dehumidifier drip pans, shower heads, toilets, and ice
machines. Water damaged carpets, ceiling panels, walls,
and paneling are prime sites for new growth if they are
allowed to stay damp. When molds, mildew, dust mites,
and bacteria are disrupted or release their spores into
the air, this results in bioaerosol formation.
Molds and mildews
develop from spores, which are in the air all around
you. As soon as spores settle in an area with the right
conditions for growth, they establish colonies, which
are often visible to the naked eye. These colonies are a
source of more spores, can cause unsightly stains, and
may release low levels of toxic chemicals called
mycotoxins into the air.
Humidifiers are
such a common source of bioaeorsols that cause health
problems that doctors now use the term humidifier
fever. Protozoa, amoebas, and strains of bacteria
have been found in humidifiers, and these are readily
released into the air with the moisture produced by
humidifiers. These have been linked to allergic
responses in sensitive people.
Mold and mildew may
be found in the ductwork of your heating or cooling
systems. If there are leaks in the ductwork, or places
where moisture and outside air get into the system, mold
and mildew can grow. Sometimes they are found in the
coils of an air conditioner or in the connection between
the unit and the ductwork. Moisture problems are worse
where ductwork insulation is on the inside as opposed to
the outside of the duct. The insulation's porous surface
collects dust and moisture. Mold and mildew may also
grow on dirty furnace and air conditioning filters.
Plumbing leaks and dampness in attics, basements, and
crawl spaces can increase humidity inside your home and
promote the growth of agents that will be released as
bioaerosols. Bathrooms without outside-vented exhaust
fans, combustion appliances like kerosene space heaters,
drying laundry indoors, and venting clothes dryers to
attics or crawl spaces can also increase the humidity
levels in your home.
Dust mites and
their waste products are the most common allergens in
indoor air. Dust mites eat human and pet skin (dander)
as it is shed. It has been estimated that we shed about
seven million cells per minute! Dust mites live in rugs
and carpets, sheets, mattresses and pillows, and
upholstered furniture. Ten to 15 percent of people are
allergic to dust mites. Of the people who have other
allergies, 40 percent are also allergic to dust mites.
What measures can be taken to control bioaerosols in the
home?
First, lower the
relative humidity in your home, basement or crawl space,
and attic. Relative humidity is the amount of moisture
in the air at a given temperature. You may want to see
Identifying and Correcting Moisture
Problems in Homes. The humidity fluctuates in your home,
depending on:
-
How warm or cool the air is indoors.
-
How many moisture-producing activities (drying
clothes indoors, showers) are taking place.
-
Whether there is a constant source of moisture
(leaks, damp foundations and attics).
-
How much moisture is being vented to the outside.
If you can keep
relative humidity below 50 percent, you can reduce
problems with dust mites, mold, and mildew. A hygrometer
can be used to measure indoor humidity levels. You can
buy a hygrometer from some nursery or garden stores, and
from hardware stores.
There is little
medical research supporting the use of a humidifier, so
try to avoid using one. If your home is extremely dry
and you must use a humidifier, a steam vaporizer or warm
mist humidifier causes fewer problems. Do not humidify
indoor air to a relative humidity level higher than 50
percent.
Ultrasonic and cool
mist (impeller-type) humidifiers can send microorganisms
from their water tanks into the air. Ultrasonic
humidifiers use sound vibrations to create a cool mist.
Impeller humidifiers create a cool mist by means of a
high-speed rotating disk. If you do use a humidifier:
-
Empty the tank, wipe all surfaces dry, and refill
the water in portable humidifiers each day.
-
Clean portable humidifiers every third day. Unplug
the humidifier before cleaning and follow the
manufacturer's recommendations on the use of
cleaning agents or disinfectants.
If you have no
specific instructions on cleaning your humidifier, use a
3 percent solution of hydrogen peroxide. Never use the
humidifier with any of the cleaning agent or
disinfectant in the tank. Rinse the tank thoroughly
several times with tap water to keep cleaning or
disinfecting chemicals out of the air.
How can I control the causes of bioaerosols?
Molds, mildew, and
dust mites are the most common causes of problems in the
home. These bioaerosols can be controlled relatively
easily.
Molds and Mildews
-
Reduce relative humidity.
-
If you find mold or mildew in your home, try to find
and eliminate sources of moisture, such as plumbing
leaks.
-
Dry the air. Use a chemical or mechanical
dehumidifier. Empty collecting (drip) pan daily.
-
Open closet doors to allow air to circulate. Use a
40-watt light bulb to dry and heat air in closets.
-
Vent bathrooms and clothes dryers to the outside.
-
Do not use humidifiers.
-
Trim back trees and shrubs around the house to
reduce shade.
-
Remove debris from your yard, roof, and gutters.
-
Clean mold and mildew growth from walls with water
mixed with chlorine bleach, diluted three parts
water to one part bleach. Commercial products can
also remove mildew and mold. Follow product
instructions carefully. Very moldy items should be
replaced.
-
Change heating and cooling system filters monthly.
-
Vacuum air return covers or screens regularly.
-
Check air conditioners for mold before each cooling
season and have coils cleaned as needed.
-
Have heating/cooling system ductwork checked for
loose insulation, leaks, or signs of condensation
where the system enters the house. Insulate ducts on
the outside of the ductwork.
-
Air cleaners and filters are other options.
Electronic and hePA (high efficiency particulate
absolute) cleaners and filters are best at taking
mold, mildew, and dust out of the air.
-
Make sure that crawl space vents work and are not
blocked. If your cooling ductwork runs through the
crawl space, consider closing crawl space vents
during summer cooling months.
-
Using vent fans in crawl spaces during the summer
when humidity is high may increase the relative
humidity in the crawl space and inside the home. Use
fans only when outside humidity is well below 50
percent.
-
Mechanical dehumidifiers reduce humidity in
basements, but they should not be used in crawl
spaces when vents are open.
-
Heating/cooling contractors or duct cleaning firms
can clean the ductwork in your home to reduce mold
and mildew growth.
Duct cleaning may
involve compressed air-washing, vacuuming and/or
scrubbing of duct surfaces. Some firms advertise
disinfectants and sealants to prevent further fungal
growth. It is uncertain whether these processes are
appropriate for most homes. Have microbial contamination
verified by an industrial hygienist or other
environmental testing agency before sanitizing products
are used in your ductwork. Commercial fogging or misting
agents should not be used because of possible health
problems from breathing these chemicals. Use of a
sealant in the ductwork is generally not appropriate
unless the mold, mildew, or dust source has been
removed.
Dust Mites
It is not known how
well any single measure controls dust mite populations.
However, it is known that effective mite control
requires that relative humidity be maintained below 50
percent. In addition, since you spend about a third of
each day in your bedroom, concentrate your efforts
there.
-
Wash sheets, pillowcases, and mattress covers
frequently in hot soapy water. If someone in your
family is allergic to dust mites, buy special vinyl
covers for the pillow and mattress.
-
Ordinary vacuuming does not remove or reduce mite
populations. Mites are so tiny that they pass
through the vacuum cleaner bag. High-efficiency
filters for vacuum cleaners may be used in place of
conventional filters.
-
Remove stuffed animals and objects that collect
dust. If carpeting is used, short-pile is best.
-
Some new products may help reduce dust mite
populations. Ask your doctor about control solutions
for upholstered furniture and bedding.
SUMMARY. Bioaerosols,
such as mold, mildew, and dust mites, are commonly found
in indoor air. Control measures include reducing sources
of moisture, reducing the relative humidity, and
removing materials which contribute to the growth of
these agents. Make your house a healthier house. Check
periodically for moisture problems and maintain the air
handling systems and filters.
For more
information, see
Air Filters and Cleaners,
or Identifying and Correcting
Moisture Problems in Homes.
Definition of Terms
Allergens --
medical term for foreign proteins that cause allergic
reactions in susceptible individuals
Biocides -- chemicals or processes that kill
living cells
Dander -- skin and hair fragments shed by humans
and other animals
Disinfection -- process of killing
disease-causing organisms
Dust Mites -- microscopic organisms that feed on
human and animal dander
Hygrometer -- instrument used to measure relative
humidity
Mycotoxins -- toxic substances produced by fungi
Sanitizing -- process to reduce the number of
disease-causing organisms
Prepared by Dr.
Sandra A. Zaslow, Extension District Director, and
Dr. Mary Beth Genter, Extension Leader, Toxicology
This publication has been issued
in print by the North Carolina Cooperative Extension
Service as publication FCS-360-5 (January 1993).
Published by
North Carolina Cooperative
Extension Service
North Carolina State University,
Raleigh, N.C.
Distributed in furtherance of the
Acts of Congress of May 8 and June 30, 1914. Employment
and program opportunities are offered to all people
regardless of race, color, national origin, sex, age, or
disability. North Carolina State University, North
Carolina A&T State University, U.S. Department of
Agriculture, and local governments cooperating.
Electronic Publication Number
(June 1995--JMG)
