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"A Brief Guide to Mold, Moisture, and Your Home"
Mold growing outdoors on firewood. Molds come in many colors; both white and black molds are shown here.
Click on the image for larger version.
Magnified mold spores
Molds gradually destroy the things they grow on. You can prevent damage to your home and furnishings, save
money, and avoid potential health problems by controlling moisture and eliminating mold growth
* Why is mold growing in my home?
* Can mold cause health problems?
* How do I get rid of mold?
* The key to mold control is moisture control.
* If mold is a problem in your home, you should clean up the mold promptly and fix the water problem.
* It is important to dry water-damaged areas and items within 24-48 hours to prevent mold growth.
Why is mold growing in my home?
Molds are part of the natural environment. Outdoors, molds play a part in nature by breaking down dead organic
matter such as fallen leaves and dead trees, but indoors, mold growth should be avoided. Molds reproduce by
means of tiny spores; the spores are invisible to the naked eye and float through outdoor and indoor air. Mold
may begin growing indoors when mold spores land on surfaces that are wet. There are many types of mold, and
none of them will grow without water or moisture.
Can mold cause health problems?
Molds are usually not a problem indoors, unless mold spores land on a wet or damp spot and begin growing.
Molds have the potential to cause health problems. Molds produce allergens (substances that can cause allergic
reactions), irritants, and in some cases, potentially toxic substances (mycotoxins). Inhaling or touching mold or
mold spores may cause allergic reactions in sensitive individuals. Allergic responses include hay fever-type
symptoms, such as sneezing, runny nose, red eyes, and skin rash (dermatitis). Allergic reactions to mold are
common. They can be immediate or delayed. Molds can also cause asthma attacks in people with asthma who are
allergic to mold. In addition, mold exposure can irritate the eyes, skin, nose, throat, and lungs of both
mold-allergic and non-allergic people. Symptoms other than the allergic and irritant types are not commonly
reported as a result of inhaling mold. Research on mold and health effects is ongoing. This brochure provides a
brief overview; it does not describe all potential health effects related to mold exposure. For more detailed
information consult a health professional. You may also wish to consult your state or local health department.
How do I get rid of mold?
It is impossible to get rid of all mold and mold spores indoors; some mold spores will be found floating through
the air and in house dust. The mold spores will not grow if moisture is not present. Indoor mold growth can and
should be prevented or controlled by controlling moisture indoors. If there is mold growth in your home, you
must clean up the mold and fix the water problem. If you clean up the mold, but don't fix the water problem, then,
most likely, the mold problem will come back.
From the EPA Website
Testing For Mold
MDH prepared this fact sheet to explain why it usually does not support mold testing as the first response to
indoor air quality concerns and to help people better understand what mold testing can and cannot be expected to
do. Contrary to much currently popular opinion, mold testing is often not an appropriate or effective way to
answer many of the questions that lead people to ask for it. In a great deal of the cases that come to MDH’s
attention, people seeking mold testing really need a thorough investigation into moisture problems and the
damage it can cause – often times this is something they can do on their own.
* Limitations of Mold Testing
* What Testing Cannot Do
* Finding a Mold Problem
* Where Can I Get More Information On Indoor Air Quality Issues?
Limitations of Mold Testing
There are many testing methods that can detect molds. They can be used to find mold particles suspended in air,
in settled dust, or growing on surfaces of building materials and furnishings. Some methods can identify a
portion of the types of live (viable) molds in a sampled environment, but these may also miss or undercount those
are not live or won’t grow well on the nutrients used to incubate the sample. Other methods are better able to
characterize the total amount of molds in a sample (including the non-living portion), but not very good for
identifying the specific types of molds. Even tests that are done well only give a partial estimate of the amount and
types of molds actually collected in a sample or in the sampled environment.
It is vital to appreciate that a test result only gives a “snap-shot” estimate for a single point in time and a single
location – how well it represents other locations and times is uncertain since the amounts and types of mold in
the environment is always changing. This variability can be especially large for airborne molds, with significant
changes occurring over the course of hours or less. Caution must also be used in interpreting surface testing
results, since mold growth or deposition may not be uniform over an area and may increase or decrease as time
passes. Unless many samples are taken over a period of time and the investigator has been mindful of building
operations and activities during the testing, the results might not be very representative of typical conditions. On
the other hand, tests reflecting typical conditions may also miss evidence of problems that only occur
Despite these limitations, there are situations where mold testing by skilled investigators may be valuable – for
example, to “justify” remediation expenses or to document that cleanup has met expectations. In some cases, tests
can also provide clues that may help find hidden mold, but the growth still has to be found by looking for it so that
it can be removed. Experienced investigators should evaluate whether testing is warranted and if they are ethical,
they should advise against testing whenever the problem can be corrected without it. Testing may be useful as
part of an investigation, but it is never a substitute for a thorough visual inspection.
Doing mold testing well is often expensive. Consumers should recognize that if the testing is not needed or it is
done poorly, their money is being wasted instead of being used to make repairs necessary to solve the problem. It
is up to consumers to protect their own interests when they hire someone to perform mold testing. MDH advises
people to attempt to investigate potential mold problems on their own first. The basic goals of any mold
investigation are always twofold: 1) find the locations of mold growth, and 2) determine the sources of the
moisture. If these can be answered by simpler or more cost-effective methods (see Finding a Mold Problem below
or the Mold in Homes fact sheet), mold testing is probably not a wise use of resources.