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.
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.
Mold is a serious health hazard in the home environment,
as it produces allergens, irritants, and in some cases, potentially toxic
substances. Further, mold can trigger respiratory problems such as asthma
in vulnerable and allergic populations. Therefore, preventing and eliminating
mold problems is a crucial part of ensuing quality housing conditions.
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 materials.
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.
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
In addition to preventative measures,
visual inspections for mold should be performed periodically for the early
detection of potential problems. The most reliable way to identify a mold
problem is through visual inspection.
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.
Mold may be clearly visible or it may be hidden under furniture
and carpets, in cabinets, and in crawlspaces or attics. When
assessing mold problems in the home environment, it is important to know
such potential hiding places and visually inspect all likely areas that
are reasonably accessible. In some cases, mold will not be discovered
even after searching typical hiding places, but a musty odor or related
health problems will indicate a mold problem. In these instances, mold
may be hidden on the backside of such materials as drywall, wallpaper,
paneling, and carpet pads or inside wall cavities and ductwork. Investigation
of such hidden mold problems is more complicated as actions such as peeling
off wallpaper may disturb the mold and cause widespread dispersal of mold
spores. Expert assistance may be required for such disruptive actions.
Use the right safety equipment during inspections. 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.
Special sampling techniques or tests may be useful. Because
all molds should be treated similarly (safely removed, while addressing
underlying moisture problems), there is no need to identify mold by type
prior to remediation. However, bulk or surface sampling may be helpful
in identifying specific mold contaminants in connection with a medical
evaluation or in confirming the presence of mold if a visual inspection
is unclear. Bulk sampling involves removing and collecting visible mold
from surfaces, while surface sampling involves wiping a surface or stripping
it with tape to collect specimens.
Airborne fungal testing is rarely appropriate but may be useful if, for
example, building occupants are experiencing symptoms that seem to be
mold-related, and a visual inspection and sampling have failed to locate
mold. Airborne testing does not provide reliable data on the average mold
content in a home—instead, it provides a “snapshot”
of mold levels, which vary considerably over the course of hours, days,
weeks, and months. Airborne fungal tests also are expensive and there
currently are no standards for determining whether measured fungal concentrations
are safe. Extensive airborne testing should be reserved for specialized
cases, such as when health problems persist in a complex building environment
with no discernable source of the problem. In such a setting, expert assistance
should be engaged.
The Alliance has informative materials and tools for low-cost assessments
of mold and moisture, in English
from its past project, the Community Environmental Health Resource Center.
Controlling mold problems in the home environment is largely dependent
on controlling the level of moisture in the home, because mold cannot
grow without moisture. Further, excessive moisture in the home is cause
for concern as it can also cause or contribute to structural home damage
and other housing hazards to human health such as cockroaches,
and peeling lead paint.
Fortunately, there are ways to prevent and control excessive moisture,
and therefore mold growth, in the home environment—both practical
measures for residents as well as precautionary measures during construction
or renovation. Please visit the
Moisture page for additional information such as practical
tips, telltale signs, and likely sources of moisture both inside and outside
The New York City Department of Health & Mental Hygiene and the U.S.
Environmental Protection Agency have developed separate but complementary
guidelines for assessing and remediating mold in indoor environments.
These guidelines contain detailed recommendations on the appropriate remediation
activities for varying sizes and locations of mold contamination in various
The NYC Guidelines contain five levels of mold remediation protocols.
The most basic techniques apply to areas of 10 square feet or less, and
include training workers on safe cleanup methods; protecting workers with
disposable respirators, gloves, and goggles; vacating people from the
work area; suppressing dust; removing and disposing of contaminated items
that cannot be cleaned; and final cleaning of work areas and work area-egress
locations. In addition to containing more protective measures such as
containment for larger mold problems, the Guidelines also address remediation
of HVAC systems.
EPA advises that if the moldy area is less than 10 square feet in total
size, non-professionals can usually manage the cleanup by following some
basic precautions and procedures. Larger jobs may require the services
of a contractor who should have prior experience cleaning up mold.
When a manageable mold problem is identified
in the home environment, the following are some basic steps that individuals,
landlords, and homeowners can take to remove the mold:
the moisture source immediately. Mold cannot grow without
water; therefore, controlling underlying moisture problems must be an
integral part of removing mold.
- Wear gloves, goggles, and appropriate respiratory
protection during all mold remediation activities. Both EPA and New
York City recommend the N-95 respirator available on the Internet and
at most hardware stores for approximately $12-25.
- Take photos of the moldy surfaces. These may be
useful in the future should the need to document the problem arise.
- Determine if it is possible to clean the moldy
area or not. Non-porous and semi-porous materials (e.g. metals, glass,
hard plastics, wood, and concrete) can generally be cleaned and reused.
Porous materials (e.g. fabrics, ceiling tiles, insulation, wallboard)
may be cleaned, but it is preferable that they be removed and thrown
away, as it is extremely difficult to ensure complete removal of the
- Remove belongings from the clean-up area.
- Clean the moldy area as soon as possible with
either a detergent/soapy water solution or a baking soda and vinegar
solution. Thoroughly dry the area and immediately dispose of all sponges
or rags used in both the cleaning and drying process. Chemicals such
as chlorine bleach are not recommended for routine mold cleanup.
- When finished cleaning the visible mold area,
clean all nearby surfaces and scrub or vacuum the floor.
- Make sure the area is well ventilated
until all surfaces are dry.
- Regularly check the area for signs of recurring
water damage and new mold growth. If the mold returns, it may indicate
that the underlying water problem has not been appropriately addressed.
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.
To find out more, see the Alliance's pages on selected
state and local legislation and existing
federal policy regarding mold and other hazards.