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---
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.
Toxicological evidence 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
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.
the basis of this review, the following guidelines were formulated.
dampness and microbial growth on interior surfaces and in building
structures should be avoided or minimized, as they may lead to adverse
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.
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.
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.
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.
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
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 microbial contamination.
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.