» Indoor Air Quality
Indoor Air Quality
Context - Air pollution – be it indoors or outdoors – is a major environmental health concern as it can lead to serious health effects, such as respiratory diseases, including asthma and lung cancer.
Much progress has been made in Europe in improving outdoor air quality and limit values have been set for several pollutants. However, indoor air quality also requires attention because this is where we spend most of our time.
Which indoor air pollutants raise concern? How can indoor air quality be determined?
An assessment by the European Commission Scientific Committee on Health and Environmental Risks (SCHER)
1. Introduction – assessing health risks of indoor air pollution
Several household cleaning products emit chemicals
Indoor exposure to air pollutants may occur in both private and public
indoor environments such as homes, offices, schools and transport
Some indoor air pollutants come from the outside, but
most are released inside the building, for example when cleaning or when
burning fuel for cooking and heating. Furniture and construction
materials can also emit pollutants. Dampness and lack of ventilation may
further increase indoor air pollution.
Because indoor air can contain a mixture of many different pollutants,
it is very difficult to
assess the associated risks to
health. Moreover, there is no such thing as a “typical indoor
This opinion considers how health risks of indoor air pollutants are
currently evaluated and how they should be assessed in the future,
taking into account simultaneous exposure to multiple pollutants and
particularly vulnerable groups of
population such as children,
pregnant women and elderly people.
2. What are the main factors in indoor air quality?
Pets and pests are sources of allergens
Certain chemicals from household products and home
appliances are known to irritate the eyes, nose and throat. However, for
many chemicals present in indoor air information is lacking on possible
health effects of long term exposure, such as
cancer or reproductive
naturally in parts of Europe. It can get inside buildings and may lead
to lung cancer.
Suspended particles can cause harmful effects on
health, particularly on the respiratory system.
Microbes, such as
viruses, can contribute to the
development of asthma and
Pets and pests such as dust mites, cockroaches, and
mice, are important indoor sources of
Low humidity causes eye irritation, dryness of the
skin and the nose, and rashes, while high humidity fosters the growth of
moulds and dust mites.
Insufficient ventilation, one of the most important
factors in poor indoor air quality, may affect health and work
Indoor temperatures that are too high or too low are
unpleasant and can be unhealthy.
3. How can scientists determine whether indoor air pollutants pose a health risk?
To determine whether pollutants may cause health effects, it is
necessary to consider four aspects:
- Toxicity of pollutants and their concentrations
in indoor air. Indoor air can for instance contain organic
compounds, particles, or
microbes that may cause
allergies or other health
- Exposure. People are mainly exposed to air
pollutants when breathing but may also be exposed via other routes,
such as dust ingestion. Since
exposures can vary, even very low and very high exposures should be
considered and not only average ones.
- Exposure-response relationships.
To assess the risk posed by a
given pollutant, it is important to know how the body responds to
different concentrations in air. Health effects observed in people
who have been exposed to pollutants at work are valuable in
determining the risks posed by a particular pollutant. However, such
findings may not be directly applicable to the general
- Risk characterisation. In the final step of
the risk assessment process,
all the collected scientific evidence is analysed to determine the
probability that a specific pollutant will cause illness.
4. Are certain people more vulnerable than others to indoor air pollution?
Some people are more vulnerable than others to indoor air
Credit: Stephan Czuratis
Population groups that are
potentially more vulnerable than
others to indoor air pollution are children, pregnant women, elderly
people, and people suffering from
cardiovascular or respiratory
Depending on their age, children may be more
vulnerable than adults to certain
toxic substances, like lead and
tobacco smoke. Even at low levels, air pollutants may disrupt the
development of their lungs, cause cough,
bronchitis and other respiratory
diseases, and make asthma worse.
Factors other than age and presence of
cardiovascular or respiratory
diseases that may render some people more
genetic traits, lifestyle,
nutrition and other health problems.
5. Why are the combined effects of indoor air pollutants hard to measure?
Like outdoor air, indoor air contains a complex mixture of pollutants
(chemical substances, allergens and
microbes) from different sources that changes with time.
Findings on the health effects of single air pollutants cannot
necessarily be extended to mixtures. Indeed, different chemicals may
interact with each other and cause more (or less) harmful effects than
the sum of the effects caused by each chemical separately. Very little
is known about the combined effects of indoor air pollutants.
Risk assessments which take into
account the combined exposure and cumulative effects of the pollutants
in indoor air are seldom possible. Nonetheless, the possibility of
combined effects should be considered in the
risk assessment taking a
6. Which chemicals found in indoor air are causing the most concern?
Tobacco Smoke contains several types of harmful
Credit: Vildan Uysal
Among the combustion products that are generated by heating systems
and other home appliances using gas, fuel, or wood,
(NO2) are of special concern.
Tobacco smoke contains several types of harmful
pollutants, including benzene and
fine and ultrafine particles. In
adults, passive smoking can cause
irritation, aggravated respiratory symptoms, and
coronary heart disease. In
children, it can lead to
sudden death syndrome and middle
naturally in certain regions. It can get inside buildings and may lead
to lung cancer.
Lead, which is still present in paintwork of some
old houses, is harmful to children even at low level exposure.
which are often used against insects in the home, can affect the
development of the nervous system
and could be of concern for children.
Volatile organic compounds
(VOCs) such as
benzene, formaldehyde and naphthalene
which are known to have health effects are emitted by many consumer
products. VOCs may react with ground-level
ozone to form
secondary pollutants that can cause
irritation. Altogether, the concentrations of VOCs and ozone causing
mixture effects are as yet poorly known.
7. What household chemicals and products can pollute indoor air?
Certain paints emit chemicals
Credit: Daniel Case
Several household consumer products emit chemicals into air, for
instance cleaning products, floor care products, furniture and household
fabrics, air fresheners, glues, paints, paint strippers, personal care
products, printed matter, electronic equipment, candles and incense.
Some studies show a link between the use of consumer products and
adverse health effects. However, it is not clear to what extent
pollutants are responsible for the observed effects because other
factors may also contribute to them.
A recent study investigated the emissions of chemicals from a large
number of different consumer products. Although typical levels in indoor
air were in most cases acceptable, in some occasions, accepted limits
8. Why is dampness in buildings a health concern?
Humidity promotes the growth of moulds
The majority of the health effects linked to dampness and moisture of
buildings are those of the respiratory system. They range from
irritation of mucous membranes,
respiratory symptoms, and infections to diseases such as
allergy. However, it is still not
known precisely how dampness leads to these symptoms and which are the
main substances responsible.
Humidity problems in buildings may originate from leaks, condensation,
or the ground. Excess humidity promotes the growth of
micro-organisms such as
bacteria that lead to release of
pollutants into indoor air.
Inadequate ventilation may increase humidity and the levels of
Further research is needed to assess how serious or widespread the
problem of building dampness and moisture is at EU level.
9. What kind of research on indoor air quality is needed?
It is necessary to investigate how people are exposed to pollutants
in indoor air
The data available for
risk assessment of indoor air
pollution are scarce and often insufficient. Information is available on
the concentrations in indoor air of some well-known pollutants but is
lacking for others whose effects are unclear. Measurements of outdoor
air quality cannot be extrapolated to predict the concentrations in
Monitoring of indicators other than concentrations may be helpful, for
instance ventilation rates, general cleanliness, and signs of dampness.
The development of health-based guideline values is recommended for key
Existing data on exposure to indoor pollutants and
information on risk assessment
strategies should be collected and organised.
Research is needed to identify the main sources of indoor pollutants,
including in damp and water-damaged buildings. In addition, it is
necessary to investigate how people are exposed to pollutants in indoor
air and how the exposure levels could be measured or estimated using
There is a need for research on the health effects of
mixtures of pollutants and of less well known indoor air pollutants such
as microbes. The contribution of indoor air pollutants to childhood
respiratory diseases, as well as the
especially in vulnerable groups,
should also be investigated further.
Existing measurement standards should be validated and harmonised.
10. Conclusions and recommendations
Assessing the health risks of indoor air pollution is very difficult
as indoor air may contain over 900 chemicals, particles and biological
materials with potential health effects. Factors like ventilation,
cleaning conditions, building characteristics, products used in
households, cultural habits, climate and outdoor environment all
influence indoor air quality. Therefore, large variations can be
expected across the EU.
The European Commission Scientific Committee on Health and
Environmental Risks (SCHER)
- The principles used in the EU for
risk assessment of chemicals
should also be applied to indoor air.
- More research and data are needed, particularly on particles
volatile organic compounds from
consumer products, building dampness, levels of exposure, and
effects on vulnerable
- Gaps in knowledge should be addressed by European-wide
(see question 9)
- Indoor air pollutants of particular concern are
environmental tobacco smoke,
radon, lead and
The SCHER also
- Data on combined effects of indoor pollutants should be
- All possible
routes of exposure should be
- Health-based guideline values for key pollutants and other
practical guidance should be developed.
- The impact of indoor exposure should be considered when
evaluating the health effects of outdoor air pollution.
- All relevant sources known to contribute to indoor air
pollution should be evaluated.