World Health Organization Dampness
and Mold Report
The World Health Organization in its report WHO Guidelines for
Indoor Air Quality:
Dampness and Mould, published July 16, 2009, reached the
following conclusions and recommendations about the
health effects of human exposure to dampness and mold growth---
Sufficient epidemiological evidence is available from studies
conducted in different countries and under different
climatic conditions to show that the
occupants of damp or mouldy buildings, both houses and public buildings, are
at increased risk of respiratory symptoms, respiratory infections and
exacerbation of asthma. Some evidence suggests increased risks of
allergic rhinitis and asthma. Although few
intervention studies were available, their results show that remediation of
dampness can reduce adverse health outcomes.
There is clinical evidence that exposure to mould and other dampness-related
microbial agents increases the risks of rare conditions, such as
hypersensitivity pneumonitis, allergic
alveolitis, chronic rhinosinusitis and
allergic fungal sinusitis.
obtained in vivo and in vitro supports these findings, showing the
occurrence of diverse inflammatory and toxic responses after exposure to
microorganisms isolated from damp buildings, including their spores,
metabolites and components.
While groups such as
atopic and allergic people are particularly susceptible to biological and
chemical agents in damp indoor environments, adverse health effects have
also been found in nonatopic populations.
The increasing prevalences of asthma and allergies in
many countries increase the number of people susceptible to the effects of
dampness and mould in buildings.
The conditions that
contribute to the health risk were summarized as follows. The prevalence of
indoor dampness varies widely within and among countries, continents and
climate zones. It is estimated to affect
10–50% of indoor environments in Europe,
North America, Australia, India and Japan. In certain settings, such as
river valleys and coastal areas, the conditions of dampness are
substantially more severe than the national averages for such conditions.
The amount of water on or in materials is the most important trigger of the
growth of microorganisms, including fungi, actinomycetes and other bacteria.
Microorganisms are ubiquitous. Microbes propagate rapidly wherever
water is available. The dust and dirt normally present in most indoor spaces
provide sufficient nutrients to support extensive
microbial growth. While mould can grow on all materials, selection of
appropriate materials can prevent dirt accumulation, moisture penetration
and mould growth.
Microbial growth may
result in greater numbers of spores, cell fragments, allergens, mycotoxins,
endotoxins, β-glucans and volatile organic
compounds in indoor air. The causative agents of adverse health
effects have not been identified conclusively, but an excess level of any of
these agents in the indoor environment is a
potential health hazard.
Microbial interactions and moisture-related physical and chemical
emissions from building materials may also play a role in dampness-related
health effects. Building standards and regulations with regard to comfort
and health do not sufficiently emphasize requirements for preventing and
controlling excess moisture and dampness.
Apart from its entry
during occasional events (such as water leaks, heavy rain and flooding),
most moisture enters a building in incoming air, including that infiltrating
through the building envelope or that
resulting from the occupants’activities.
Allowing surfaces to become cooler than the surrounding
air may result in unwanted condensation. Thermal
bridges (such as metal window frames), inadequate insulation and
unplanned air pathways, or cold water plumbing and cool parts of
air-conditioning units can result in surface temperatures below the dew
point of the air and in dampness.
On the basis of this review, the following guidelines
Persistent dampness and
microbial growth on interior surfaces and in building structures should be
avoided or minimized, as they may lead to adverse health effects.
Indicators of dampness and microbial growth include the
presence of condensation on surfaces or in structures, visible mould,
perceived mouldy odour and a history of water damage, leakage or
penetration. Thorough inspection and, if necessary, appropriate measurements
can be used to confirm indoor moisture and microbial growth.
As the relations between dampness, microbial exposure
and health effects cannot be quantified precisely, no quantitative
health-based guideline values or thresholds can be recommended for
acceptable levels of contamination with
microorganisms. Instead, it is recommended that dampness and mould-related
problems be prevented. When they occur, they should be remediated because
they increase the risk of hazardous exposure to microbes and chemicals.
well-constructed, well-maintained building envelopes are critical to the
prevention and control of excess moisture and microbial growth, as they
prevent thermal bridges and the entry of liquid or vapour-phase water.
Management of moisture requires proper control of
temperatures and ventilation to avoid excess humidity, condensation on
surfaces and excess moisture in materials. Ventilation should be distributed
effectively throughout spaces, and stagnant air zones should be avoided.
Building owners are responsible for providing a healthy
workplace or living environment free of excess moisture and mould, by
ensuring proper building construction and maintenance. The occupants are
responsible for managing the use of water, heating, ventilation and
appliances in a manner that does not
lead to dampness and mould
growth. Local recommendations for different climatic regions should be
updated to control dampness-mediated microbial growth in buildings and to
ensure desirable indoor air quality.
Dampness and mould may be particularly prevalent in
poorly maintained housing for low-income people. Remediation of the
conditions that lead to adverse exposure should be given priority to prevent
an additional contribution to poor health in populations who are already
living with an increased burden of disease.
The guidelines are intended for worldwide use, to
protect public health under various environmental, social and economic
conditions, and to support the achievement of optimal indoor air quality.
They focus on building characteristics that prevent the occurrence of
adverse health effects associated with dampness
or mould. The guidelines
pertain to various levels of economic development and different climates,
cover all relevant population groups and propose feasible approaches for
reducing health risks due to dampness and
Both private and public
buildings (e.g. offices and nursing homes) are covered, as dampness and
mould are risks everywhere. Settings in which there are particular
production processes and hospitals with high-risk patients or sources of
exposure to pathogens are not, however, considered.
While the guidelines provide objectives for indoor
air quality management, they do not give instructions for achieving
those objectives. The necessary action and indicators depend on local
technical conditions, the level of development, human capacities and
resources. The guidelines recommended by WHO acknowledge this heterogeneity.
In formulating policy targets, governments should consider their local
circumstances and select actions that will ensure achievement of their
health objectives most effectively.