|Molds are simple, microscopic
organisms that can grow virtually anywhere, both in homes and
outdoors. Along with mushrooms, yeasts, and mildew, molds are
classified as fungi. Molds typically consist of a network of
threadlike filaments that infiltrate the surface on which the
mold is growing. Molds reproduce by releasing spores, which
are lightweight and small enough to travel through the air.
Spores can resist dry, adverse environmental conditions, allowing
them to outlive the mold that produced them.
Molds play an important ecological role in breaking down dead organic
matter and returning nutrients to the environment. They require moisture
and food to grow, and they typically thrive in warm, moist environments.
Moisture is the key factor determining mold growth in the home, influencing
both the types of mold present and the extent of mold colonization. A
variety of materials found in the home, including insulation, wallpaper,
glues used to affix carpet, backing paper on drywall, dust, and dirt,
can serve as a food source for mold. Mold colonies can go dormant under
adverse conditions and revive when favorable conditions return.
Mold growth often appears as green, gray, black, brown, or other discoloration.
Eventually, mold growth results in the breakdown of the substrate. More
than 1,000 types of molds have been found in US homes.
People are exposed to mold on a daily basis. Most exposures
in the home occur when occupants inhale spores or mold fragments,
which are components of household dust. They also may be exposed
when their skin comes into contact with mold-contaminated
Most people are unaffected by exposure to moderate amounts of mold. However,
mold exposure can cause allergic reactions in some people. Approximately
6-10 percent of the general population, and 15-50 percent of persons who
are genetically prone to develop allergies (atopic individuals), are allergic
to mold, according to the National Academy of Sciences. The most common
symptoms include runny nose, eye irritation, coughing, congestion, and
exacerbation of asthma in persons who have the disease. At this point,
it is unclear whether mold can cause individuals to become asthmatic.
For more information on asthma and allergies, see Asthma,
Allergies, and Respiratory Illnesses.
Some types of mold produce toxic substances known as mycotoxins, which
can cause health problems when they are inhaled, absorbed through the
skin, or ingested. One mold species may produce a number of different
mycotoxins; conversely, one mycotoxin may be produced by several different
types of mold. Mycotoxin production varies depending on environmental
conditions such as moisture level, temperature, and substrate content.
As a general matter, toxin-producing molds have higher water requirements
than most household molds, so they thrive indoors only under wet conditions.
Although the health impacts of exposure to mycotoxins in the home are
not well studied, adverse health effects have been observed in occupational
settings and in animal studies. Of course, health impacts vary depending
on the mycotoxin at issue and the nature of the exposure. Skin rashes,
fatigue, dizziness, flu-like symptoms, nausea, respiratory and eye irritation,
immuno-suppression, birth defects, lung inflammation, and cancer have
been associated with exposure to mycotoxins. Persons exposed to high levels
of mold toxins, e.g., mold remediation workers or farm workers, may be
at risk for organic toxic dust syndrome (OTDS) or hypersensitivity pneumonitis
(HP). ODTS may occur after a single, heavy exposure to mycotoxins, and
usually carries with it fever, respiratory, and flu-like symptoms. HP
is an immunological disease caused by repeated, high-level exposures to
the same agent, and can result in permanent lung damage.
Mold exposure also may lead to infections such as fungal
pneumonia in persons with compromised immune systems.
The most reliable way to identify a mold problem is through visual inspection.
According to experts with the Building Science Corporation, “If
you see mold or you smell mold, you have mold.” Since mold requires
water in order to grow, looking for water or moisture problems is usually
the best way to locate mold. This may require looking behind walls or
ceilings, under furniture, in crawlspaces and basements, or behind cabinets
and toilets. While assessing mold contamination, workers should wear gloves
and eye protection and a respirator. They also should take steps to ensure
that large amounts of mold are not released into the home from concealed
areas, by misting moldy surfaces before disturbing them or using a HEPA
vacuum attachment when cutting mold-contaminated surfaces, for example.
Although health-based standards for mold currently do not exist, it is
generally accepted that no one should live or work in an indoor environment
beset by extensive mold growth. Since mold requires moisture to grow,
mold problems can be prevented by solving moisture problems quickly and
effectively. Moisture in the home may be caused by poor ventilation, excess
condensation (due to humidifiers or unvented clothes dryers, for example),
water leaks, or floods. In the case of a flood or leak, mold growth can
be prevented if water-damaged materials are dried and cleaned and/or removed
within 24-48 hours. Additional preventative measures include regularly
checking plumbing and promptly repairing leaks; maintaining relative humidity
below 60 percent; venting clothes dryers; and installing exhaust fans
in kitchens and bathrooms vented to the outside. For more information
on addressing moisture problems in the home, see How
to Control Moisture.
If mold is obviously present, the first step in controlling the problem
is to assess the extent of the contamination. The Environmental Protection
Agency (EPA) has developed mold remediation guidelines for schools and
commercial buildings, and the New York City Department of Health (NYC)
has created assessment and remediation guidelines for fungi in indoor
environments. Both of these guidelines recommend remedial measures and
precautions calibrated to the amount of mold present.
As a general matter, the goal of mold
remediation is to remove or clean contaminated materials
in a manner that prevents mold and contaminated dust from escaping the
work area, while protecting the workers performing the remediation. The
underlying water or moisture problems must be addressed prior to or during
remediation; otherwise, mold growth will recur.
Despite the flurry of activity around the country to pass laws relating
to mold, legislation on the problem remains in the nascent stages. Currently,
there are no health-based standards for mold exposure. The EPA and NYC
guidelines set forth recommendations for safe assessment and remediation
of mold contamination, but they are not legally binding. The laws being
considered, and in some cases adopted, address a few common themes. Some
laws seek to establish committees or task forces to study the issues surrounding
mold. Other laws have sought to implement licensing schemes for mold inspectors
and/or remediators. Some laws under consideration have addressed insurance
issues, while others have sought to require disclosure of mold during
sale or lease transactions. In some cases, legislatures have focused on
indoor air quality issues in schools and public buildings.
Several states also have considered adopting more comprehensive mold
legislation, modeled in some cases on California’s Toxic Mold Protection
Act, which requires the state’s Department of Health Services (DHS)
to convene a task force to consider the feasibility of adopting exposure
limits to mold in indoor environments (and to adopt standards if feasible).
The Act also directs DHS to adopt practical standards to assess the health
threat posed by mold, develop remediation guidelines, and assess the need
for standards covering mold assessment and remediation professionals.
Landlords are required to provide written disclosure of known mold contamination
to tenants prior to entering into a lease and to provide a DHS brochure
on mold. However, these requirements do not become effective until after
the standards are adopted and DHS creates a brochure. City attorneys,
as well as code enforcement and public health officials, are authorized
to enforce the Act, which has gone largely unimplemented due to lack of
funding. In New York State, two bills have been introduced that mirror
the California Act.
See Action Agenda
for more information about legislation and regulations.
Affordable Comfort - www.affordablecomfort.org
Building Science Corporation - www.buildingscience.com/
Canada Mortgage and Housing Corporation - www.cmhc-schl.gc.ca
Environmental Health Watch, Moisture Audit of Residential
Structures - www.ehw.org/Healthy_House/HH_Moist_Audit.htm
Environmental Protection Agency, Mold Remediation in Schools
and Commercial Buildings - www.epa.gov/iaq/molds/images/moldremediation.pdf
T. Platts-Mills, J. Vaughan, M. Carter, and J. Woodfolk, Journal
of Allergy and Clinical Immunology, “The Role of Intervention
in Established Allergy: Avoidance of Indoor Allergens in the Treatment
of Chronic Allergic Diseases,” pp. 787-804 (November 2000).
US Dept. of Housing and Urban Development, Healthy Homes Issues: Mold,
External Review Draft, Version 2, October 2, 2001 - www.hud.gov/offices/lead/hhi/Mold_v2_12-01.pdf