A Brief Guide to Mold
Molds belong to the group of organisms called fungi and as such,
are neither animals nor plants. There are more than 1.5 million
fungi worldwide, not all of which are molds, but molds are found
in every environment. When moisture and oxygen are present, they
grow on organic substances by digesting plant and animal matter
for energy. Anything of organic origin may be subject to attack.
Outdoors, molds play a key role in the breakdown of leaves, wood
and other organic debris.
Molds reproduce through microscopic spores (Fig. 1). Spores are
moved in water, through the air by breezes, even by a passing
person or animal. Several fungi actively discharge spores when
environmental conditions are right. Consequently, mold spores
are found in indoor and outdoor air. Virtually every breath we
take contains mold spores.
When spores land on damp areas, they begin growing as they
digest the organic matter around them. They stain wood
structures, produce, home and garden furnishings—any product
made from plants or animals.
Most molds are harmless to humans. However, some produce
mycotoxins that affect people and animals. Individuals can
suffer allergic reactions or infections from inhaling,
ingesting, or touching mold or mold spores. An individual’s
sensitivity to a particular mycotoxin depends on his or her
innate resistance to it, how much toxin is present (its
concentration), how long a person is exposed to the mold
producing it, and whether or not it is ingested, inhaled or
touched. All these factors must be considered when associating
molds with health concerns.
One strain of mold, stachybotrys, has received considerable
media attention. It is believed to be the cause of several
health problems for people who live or work in structures with
water or moisture problems. However, the presence of mold does
not always mean harmful mycotoxins are present. Even so,
removing existing molds and preventing any new molds from
growing can avoid potential health concerns.
Molds require several specific conditions to grow. Controlling
any of the following conditions will control their development:
In Cooperation with the Nevada Department of Agriculture
Moisture is necessary in sufficient amounts for mold to develop.
In poorly ventilated spaces, organic substances absorb moisture.
Moisture contents from 25% to 75% are considered optimal for
mold development. Poor ventilation causes the relative humidity
(RH) of the air to increase, which encourages mold to grow.
Keeping an area well ventilated, especially in Nevada, reduces
the RH of the air, keeps the area dry and prevents mold growth.
Food (energy) is required for molds to flourish. Molds readily
digest proteins and starches from organic substances such as
bread, cheese, and animal products (leather, wallpaper paste,
etc.) used in home construction. Temperature is as crucial to
mold development as moisture or food. Like other organisms,
molds have a temperature range in which they develop.
Temperatures between 50 ºF and 90 ºF are optimal for mold
growth. Light affects various molds differently, particularly
sunlight or UV lamps. Ultraviolet (UV radiation) kills or
suppresses growth of many molds. Figure 2. Mold growth hidden
behind wallboard (top)
and behind wall paper (bottom).
bathroom surfaces, upholstery, drapes, mattresses, drywall,
wallboard and wood surfaces throughout a home—closets,
cupboards, walls, ceilings, attics, floors, subflooring,
basements and crawlspaces (Fig. 3).
Not every water leak or high moisture situation results in a
mold infestation. The growth of an infestation not only depends
on these four factors (moisture, food, temperature and light or
dark) but also on how long they occur together. If leaks are
found early and repaired, mold infestations can be prevented.
However, leaks left unrepaired will only encourage molds to grow
inside a home. Areas that become wet and then dry slowly may
allow ample time for mold to develop. Stop leaks and dry out
damp areas immediately to discourage mold growth.
Commonly, mold develops inside a home around windowsills and
plumbing, and in kitchens, bathrooms, basements, crawlspaces and
the attic. Leaky roofs, chimneys and poorly designed or
installed vents allow unwanted moisture to accumulate. In
Nevada, homes with poor ventilation, inadequate cross
ventilation, or without a vapor barrier over the soil in the
crawlspace can develop high humidity inside these areas. Water
will condense on rim joists, mudsills, beams and other areas
under and within a home. This encourages the development of
mold. Proper ventilation and maintenance of the attic, basement
or crawlspace prevent mold infestations.
The best approach to mold control is through prevention!
Suggestions for preventing molds in a living area, attic or
crawlspace are:
For homes with crawlspaces beneath them, make sure foundation
vents are open and unobstructed, and that adequate cross
ventilation exists. Install additional vents if necessary.
Reduce humidity in the crawlspace by eliminating the source of
moisture to the
soil under the home by draining water
away from the foundation and by
installing a vapor barrier over the soil.
Slope the ground away from building foundations and provide good
drainage to route water away from structures.
Never allow sprinklers to spray on a home or other structures.
Make sure attic vents are open and unobstructed. Install
additional vents or a roof turbine if necessary.
Fix leaky plumbing and leaks in the building envelope when they
are discovered.
Watch for condensation and wet spots, and eliminate them by
removing the source of water or increasing air circulation with
ventilation.
Vent moisture-generating appliances, such as dryers, to the
outside of the home, not into the crawlspace or attic.
Keep heating, ventilation and air conditioner’s (HVAC) drip pans
clean, flowing properly and unobstructed.
Regularly inspect the building and HVAC system and perform
maintenance as scheduled or necessary.
Fix any moisture problem as soon as possible.
Pest inspectors estimate that 10% to 15% of the homes in
northern Nevada have mold in the crawlspace. It may be less in
southern Nevada. Consider these factors to determine the
seriousness of a mold infestation.
Extent of Infestation: The number and size of mold growths. A
mold “spot” may be only the size of a quarter or larger than
several square feet. The smaller the total area infested the
better, because fewer spores will be produced.
Exposure and Location: As with any potential toxicant, the
length of exposure time and the amount or concentration of the
irritant and the sensitivity of the person to the mold affects
the severity of a potential reaction. Exposure of a person to a
mold depends upon their proximity to each other. For example, an
infestation of mold inside a bedroom would be more likely to
cause a reaction in a sensitive person due to greater exposure
than if the same mold were growing in the crawlspace under the
home.
Species of Mold: Experts estimate that there are nearly 100,000
species of mold. Molds come in a variety of colors (white,
yellowish green, green, red and black) but only a few produce
mycotoxins believed to impair health. Identifying the species is
necessary to correctly identify the mold and determine whether
or not it produces harmful mycotoxins.
Human Sensitivity: Human response to mycotoxins is variable.
Several members of a household may not be sensitive, others
moderately affected, and one or all could be hypersensitive and
unable to live with a particular mold.
Pest inspectors are not required nor are they encouraged to
report the presence of a mold as a health-related mold. This is
a separate issue. If an inspection for health related molds is
needed, it is suggested that a qualified professional be
contacted to perform the inspection. For More information please
call us.
For more information about mold, go to the following web sites:
www.cal-iaq.org/
www.epa.gov/iaq/index.html www.nvc.gov/html/doh/html/ei/eimold.html
www.nyc.gov/html/doh/html/epi/moldrpt1.html
The information presented in this publication was developed
through the cooperation of Nevada’s commercial pest control
industry, the Nevada Department of Agriculture, the United
States Environmental Protection Agency and the University of
Nevada Cooperative Extension. It is intended to provide a basic
understanding of the development of molds and the inspection
responsibilities of licensed pest inspectors who perform
wood-destroying pest inspections in Nevada. The above entities
take no responsibility for any misrepresentation or misuse of
this information.
Editing & Technical Assistance by Sue Strom,
University of Nevada, Reno
