Molds produce tiny spores to reproduce. Mold spores waft through the indoor
and outdoor air continually. When mold spores land on a damp spot indoors, they
may begin growing and digesting whatever they are growing on in order to
survive. There are molds that can grow on wood, paper, carpet, and foods. When
excessive moisture or water accumulates indoors, mold growth will often occur,
particularly if the moisture problem remains undiscovered or un-addressed. There
is no practical way to eliminate all mold and mold spores in the indoor
environment; the way to control indoor mold growth is to control moisture.
Basic Mold Cleanup
As the key to mold control is moisture control, it is important to dry water
damaged areas and items within 24-48 hours to prevent mold growth. If mold is a
problem in your home, clean up the mold and get rid of the excess water or
moisture. Fix leaky plumbing or other sources of water. Wash mold off hard
surfaces with detergent and water, and dry completely. Absorbent materials (such
as ceiling tiles & carpet) that become moldy may have to be replaced.
- Potential health effects and symptoms associated with mold exposures include
allergic reactions, asthma, and other respiratory complaints.
- There is no practical way to eliminate all mold and mold spores in the
indoor environment; the way to control indoor mold growth is to control
- If mold is a problem in your home or school, you must clean up the mold and
eliminate sources of moisture.
- Fix the source of the water problem or leak to prevent mold growth.
- Reduce indoor humidity (to 30-60% ) to decrease mold growth by: venting
bathrooms, dryers, and other moisture-generating sources to the outside; using
air conditioners and de-humidifiers; increasing ventilation; and using exhaust
fans whenever cooking, dishwashing, and cleaning.
- Clean and dry any damp or wet building materials and furnishings within
24-48 hours to prevent mold growth.
- Clean mold off hard surfaces with water and detergent, and dry completely.
Absorbent materials such as ceiling tiles, that are moldy, may need to be
- Prevent condensation: Reduce the potential for condensation on cold surfaces
(i.e., windows, piping, exterior walls, roof, or floors) by adding insulation.
- In areas where there is a perpetual moisture problem, do not install
carpeting (i.e., by drinking fountains, by classroom sinks, or on concrete
floors with leaks or frequent condensation).
- Molds can be found almost anywhere; they can grow on virtually any
substance, providing moisture is present. There are molds that can grow on wood,
paper, carpet, and foods.
Molds can trigger asthma episodes in spore-sensitive individuals with asthma.
People with asthma should avoid contact with or exposure to molds.
- Allergy & Asthma Network/Mothers of Asthmatics (AAN/MA): (800) 878-4403;
- American Academy of Allergy, Asthma & Immunology (AAAAI): www.aaaai.org
- American Lung Association: 1-800-LUNG-USA (1-800-586-4872); www.lungusa.org
- Asthma & Allergy Foundation of America: (800) 7ASTHMA; www.aafa.org
- Canada Mortgage & Housing Corporation fact sheets on mold – www.cmhc-schl.gc.ca/en/burema/gesein/abhose/abhose_50.cfm
- National Institute of Allergy and Infectious Diseases: www.niaid.nih.gov
- National Jewish Medical and Research Center: (800) 222-LUNG (5864); www.njc.org
How do molds affect people?
Some people are sensitive to molds. For these people, exposure to molds can
cause symptoms such as nasal stuffiness, eye irritation, wheezing, or skin
irritation. Some people, such as those with serious allergies to molds, may have
more severe reactions. Severe reactions may occur among workers exposed to large
amounts of molds in occupational settings, such as farmers working around moldy
hay. Severe reactions may include fever and shortness of breath. Some people
with chronic lung illnesses, such as obstructive lung disease, may develop mold
infections in their lungs.
EPA’s publication, Indoor Air Pollution: An
Introduction for Health Professionals , assists health professionals
(especially the primary care physician) in diagnosis of patient symptoms that
could be related to an indoor air pollution problem. It addresses the health
problems that may be caused by contaminants encountered daily in the home and
office. Organized according to pollutant or pollutant groups such as
environmental tobacco smoke, VOCs, biological pollutants, and sick building
syndrome, this booklet lists key signs and symptoms from exposure to these
pollutants, provides a diagnostic checklist and quick reference summary, and
includes suggestions for remedial action. Also includes references for
information contained in each section. This booklet was developed by the
American Lung Association, the American Medical Association, the U.S. Consumer
Product Safety Commission, and the EPA. EPA Document Reference Number
Allergic Reactions – excerpted from Indoor Air
Pollution: An Introduction for Health Professionals section on: Animal Dander,
Molds, Dust Mites, Other Biologicals .
“A major concern associated with exposure to biological pollutants is
allergic reactions, which range from rhinitis, nasal congestion, conjunctival
inflammation, and urticaria to asthma. Notable triggers for these diseases are
allergens derived from house dust mites; other arthropods, including
cockroaches; pets (cats, dogs, birds, rodents); molds; and protein-containing
furnishings, including feathers, kapok, etc. In occupational settings, more
unusual allergens (e.g., bacterial enzymes, algae) have caused asthma epidemics.
Probably most proteins of non-human origin can cause asthma in a subset of any
appropriately exposed population.”
Consult the Centers for Disease Control (CDC)
- CDC’s National Center for Environmental
Health (NCEH) has a toll-free telephone number for information and FAXs,
including a list of publications: NCEH Health Line 1-888-232-6789.
- CDC’s “Molds in the
The EPA publication, “A Brief Guide to Mold, Moisture, and Your Home”
, is available here in HTML and PDF formats. This Guide
provides information and guidance for homeowners and renters on how to clean up
residential mold problems and how to prevent mold growth. A printed version
will be available soon.
Biological Pollutants in
Your Home – This document explains indoor biological pollution, health
effects of biological pollutants, and how to control their growth and buildup.
One third to one half of all structures have damp conditions that may encourage
development of pollutants such as molds and bacteria, which can cause allergic
reactions — including asthma — and spread infectious diseases. Describes
corrective measures for achieving moisture control and cleanliness. This
brochure was prepared by the American Lung Association and the U.S. Consumer
Product Safety Commission. EPA Document Reference Number 402-F-90-102, January
Moisture control is the key to mold control, the Moisture Control Section
from Biological Pollutants
in Your Home follows:
Water in your home can come from many sources. Water can enter your home by
leaking or by seeping through basement floors. Showers or even cooking can add
moisture to the air in your home. The amount of moisture that the air in your
home can hold depends on the temperature of the air. As the temperature goes
down, the air is able to hold less moisture. This is why, in cold weather,
moisture condenses on cold surfaces (for example, drops of water form on the
inside of a window). This moisture can encourage biological pollutants to grow.
There are many ways to control moisture in your home:
- Fix leaks and seepage. If water is entering the house from the outside, your
options range from simple landscaping to extensive excavation and waterproofing.
(The ground should slope away from the house.) Water in the basement can result
from the lack of gutters or a water flow toward the house. Water leaks in pipes
or around tubs and sinks can provide a place for biological pollutants to grow.
- Put a plastic cover over dirt in crawlspaces to prevent moisture from coming
in from the ground. Be sure crawlspaces are well-ventilated.
- Use exhaust fans in bathrooms and kitchens to remove moisture to the outside
(not into the attic). Vent your clothes dryer to the outside.
- Turn off certain appliances (such as humidifiers or kerosene heaters) if you
notice moisture on windows and other surfaces.
- Use dehumidifiers and air conditioners, especially in hot, humid climates,
to reduce moisture in the air, but be sure that the appliances themselves don’t
become sources of biological pollutants.
- Raise the temperature of cold surfaces where moisture condenses. Use
insulation or storm windows. (A storm window installed on the inside works
better than one installed on the outside.) Open doors between rooms (especially
doors to closets which may be colder than the rooms) to increase circulation.
Circulation carries heat to the cold surfaces. Increase air circulation by using
fans and by moving furniture from wall corners to promote air and heat
circulation. Be sure that your house has a source of fresh air and can expel
excessive moisture from the home.
- Pay special attention to carpet on concrete floors. Carpet can absorb
moisture and serve as a place for biological pollutants to grow. Use area rugs
which can be taken up and washed often. In certain climates, if carpet is to be
installed over a concrete floor, it may be necessary to use a vapor barrier
(plastic sheeting) over the concrete and cover that with sub-flooring
(insulation covered with plywood) to prevent a moisture problem.
- Moisture problems and their solutions differ from one climate to another.
The Northeast is cold and wet; the Southwest is hot and dry; the South is hot
and wet; and the Western Mountain states are cold and dry. All of these regions
can have moisture problems. For example, evaporative coolers used in the
Southwest can encourage the growth of biological pollutants. In other hot
regions, the use of air conditioners which cool the air too quickly may prevent
the air conditioners from running long enough to remove excess moisture from the
air. The types of construction and weatherization for the different climates can
lead to different problems and solutions.
Moisture On Windows
Your humidistat is set too high if excessive moisture collects on windows and
other cold surfaces. Excess humidity for a prolonged time can damage walls
especially when outdoor air temperatures are very low. Excess moisture condenses
on window glass because the glass is cold. Other sources of excess moisture
besides overuse of a humidifier may be long showers, running water for other
uses, boiling or steaming in cooking, plants, and drying clothes indoors. A
tight, energy efficient house holds more moisture inside; you may need to run a
kitchen or bath ventilating fan sometimes, or open a window briefly. Storm
windows and caulking around windows keep the interior glass warmer and reduce
condensation of moisture there.
Humidifiers are not recommended for use in buildings without proper vapor
barriers because of potential damage from moisture buildup. Consult a building
contractor to determine the adequacy of the vapor barrier in your house. Use a
humidity indicator to measure the relative humidity in your house. The American
Society of Heating and Air Conditioning Engineers (ASHRAE) recommends these
maximum indoor humidity levels.
Outdoor Recommended Indoor Temperature Relative Humidity
+20 F. 35%
+10 F. 30%
0 F. 25%
-10 F. 20%
-20 F. 15%
Anne Field, Extension Specialist, Emeritus, with reference from the
Association for Home Appliance Manufacturers ( www.aham.org ).
Should You Have
the Air Ducts in Your Home Cleaned? – excerpt on duct cleaning and
mold follows, please review the entire document for additional information on
duct cleaning and mold.
You should consider having the air ducts in your home cleaned if:
There is substantial visible mold growth inside hard surface (e.g., sheet
metal) ducts or on other components of your heating and cooling system. There
are several important points to understand concerning mold detection in heating
and cooling systems:
- Many sections of your heating and cooling system may not be accessible for a
visible inspection, so ask the service provider to show you any mold they say
- You should be aware that although a substance may look like mold, a positive
determination of whether it is mold or not can be made only by an expert and may
require laboratory analysis for final confirmation. For about $50, some
microbiology laboratories can tell you whether a sample sent to them on a clear
strip of sticky household tape is mold or simply a substance that resembles it.
- If you have insulated air ducts and the insulation gets wet or moldy it
cannot be effectively cleaned and should be removed and replaced.
- If the conditions causing the mold growth in the first place are not
corrected, mold growth will recur.