Air quality indoors: why ventilation is important

The air within many homes in Germany is contaminated with pollutants, for example mold, particulates and radon. Discover which other substances can affect indoor air quality and how you can protect yourself.

At a glance

  • Pollutants in the indoor air primarily come from building materials, cleaning agents and furniture.
  • Pollutants can also arise due to moisture and combustion processes such as cooking or smoking.
  • Poor air quality in homes can, among other things, promote the development of respiratory diseases, allergies and cancer.
  • In Germany, health conditions that are directly attributable to indoor air are rare though.
  • Simple measures such as impact ventilation (briefly opening windows) can improve indoor air quality.

Note: The information in this article cannot and should not replace a medical consultation and must not be used for self-diagnosis or treatment.

An open window. Trees and blue sky are visible in the background.

What influences indoor air quality?

Indoor air is usually not completely free of harmful substances. Cooking, cleaning and other activities release pollutants into the air in the form of gases, vapors and dust. In particular, building materials and new furniture often release harmful chemicals into the air. Smoking also creates pollutants.

In addition, particulates from contaminated outside air can be brought indoors.

However, pollutants can normally be reduced to safe levels by taking certain crucial protective measures.

Pollutants can normally be reduced to safe levels by taking certain crucial protection measures.

Where do indoor pollutants come from?

The pollutants in indoor air can come from very different sources both within and outside buildings.

Chemical substances

Chemical substances can be released from building products, joints, furniture, cleaning agents and care products, especially during renovations. Examples of harmful chemicals include formaldehyde, terpenes, asbestos and polychlorinated biphenyls. The latter are primarily found in old building materials.

Radioactive substances

The radioactive gas radon is produced from the uranium in soil and mainly accumulates in the lower floors of buildings. It is formed in rocks that contain uranium. The prevalence of these differs from region to region but they are primarily found in the middle and high mountains. As a result, higher concentrations of radon are often found in these areas.

Exhaust gases and particulates

Outdoor air can contaminate the indoor air, for example through exhaust gases and particulates. This can especially be the case if people live on the ground floor near a busy road. In addition, all indoor combustion processes release pollutants into the air. This particularly applies to smoking but also to the use of fireplaces and candles as well as to cooking, especially when doing so with gas.


Various allergy-causing substances (allergens) get into the indoor air: dust mites can be found almost everywhere in the home, especially in textiles and in the bed, and are stirred up by drafts. Many people have allergic reactions to these. Pet allergens are another example. These sometimes spread through tiny, floating particles. As a result, they too become distributed in the indoor air.

Excessively high humidity indirectly affects the air by causing mold to form. This particularly occurs as a result of people showering, washing and drying laundry. Mold spores are stirred up by air movements and distributed through the room. Mold can cause allergies and respiratory diseases.

Infectious aerosols

A further risk in relation to indoor air is that of infectious aerosols, which enable the transmission of various pathogens – especially bacteria and viruses. Aerosols are microscopic droplets that can contain pathogens. These particles are released into the air when breathing, speaking and singing. They are so light that they float in the air for a long time. When people are infected with a virus, such as the SARS-CoV-2 coronavirus, the indoor air particularly in poorly ventilated areas can become contaminated with the virus. If a healthy person inhales this air, there is a higher risk of infection. 

Overview of pollutants and their sources

A detailed overview of key pollutants and their sources can be found in this table, taken from an overview article from the German public health journal “Bundesgesundheitsblatt” on indoor pollutants.

What are the health risks?

The health risks of pollutants in indoor air can vary greatly in different buildings and different regions of Germany. The risks particularly depend on the materials installed, the furniture and the residents’ behavior. The risk of illness only increases if the pollutants reach a certain concentration.

Luftschadstoffe in Innenräumen können unter anderem folgende Erkrankungen auslösen: Allergien, eine Schwächung der Immunabwehr, Krebs, Reizungen der Haut oder Augen, Erkrankung der Atemwege, Virusinfektionen.

Poor indoor air quality can increase the risk of the following illnesses and health conditions:

  • allergies: for example due to dust mites, pets and mold
  • immune deficiency: for example due to mold and polychlorinated biphenyls
  • cancer: for example due to radon, particulates and formaldehyde
  • skin, eye, nose and throat irritation as well as headaches: due to various chemical compounds
  • respiratory system disorders: especially due to nitrogen dioxide (exhaust gases and gas stoves), carbon monoxide (exhaust gases, wood-burning and coal-fired stoves), mold and particulates
  • airborne viral infections

Every year, about 3.8 million people worldwide die as a result of indoor air pollution. 27 percent of these die from the consequences of pneumonia, 27 percent of coronary heart disease, 20 percent of chronic-obstructive pulmonary disease (COPD), 18 percent of a stroke and 8 percent of lung cancer.

Who is particularly at risk?

Infants, children and older people as well as people with respiratory conditions, heart conditions or an immunodeficiency are at higher risk from polluted indoor air. One reason for this is that their immune system is often weaker.

In addition, pregnant women should take care not to expose themselves to excessively high levels of air pollution.  The pollutants can be passed on and pose health risks to the unborn child. 

How can people protect themselves?

Impact and cross-ventilation

Ventilation plays a key role in improving the air quality in homes. This is particularly important just after renovations as it effectively reduces the level of gaseous chemical substances. Ventilation is also important after cooking, showering and cleaning, as well as when smoking or burning candles.

As a general rule of thumb, homes should be ventilated for at least 5 minutes at least once an hour. Impact and cross-ventilation are particularly effective. That means opening the windows wide, ideally at both sides of the home as this enables a through-draft.

The risk of contracting viruses like SARS-CoV-2 can also be reduced through ventilation. In addition, good coughing and sneezing etiquette should be observed in indoor areas, which means doing so into the crook of the arm. This distributes fewer viruses around the room.


Ventilation can only reduce the levels of substances that float in the air. It cannot remove heavier substances, which often combine with house dust. Any dust should therefore be regularly wiped away. A damp cloth usually suffices to this end; cleaning agents are not necessarily required.

Suspected high levels of pollutants

If you have health problems that may be caused by air pollutants in your home, start by consulting your family doctor. Try to find the source of the pollutant and remove or minimize it. If necessary, a pollutant analysis by an accredited institute can help.

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