We spend most of our time indoors. Our activities, the objects and the materials that surround us release substances into the air that can be harmful to health. 

Where does indoor air pollution come from?

Indoor air pollution can be put down in part to changes in the environment and in our way of life. We spend most of our time inside buildings that are increasingly insulated and therefore more confined. Numerous chemical, microbiological and physical pollutants accumulate in this stale indoor air.

Insufficient ventilation and fresh air intake encourage the containment and accumulation of pollutants in the indoor air, insufficient cleaning promotes the accumulation of dust and damp fosters the development of germs.

Chemical pollutants

Chemical pollutants can take the form of gases, vapours, aerosols and particles. Chemical pollutants include:

  • smoke from cigarettes
  • carbon dioxide (from human breathing)
  • carbon monoxide and nitrogen dioxide (poor maintenance of combustion equipment)
  • volatile organic compounds (building materials, furniture, maintenance products, renovation products, paints, glues, solvents, varnishes, wax, scented candles, incense, etc.) 
  • flame retardants (upholstered products, electronic materials, textiles, synthetic foams)
  • etc.

DID YOU KNOW? Here are some names of volatile organic compounds (VOC) to look out for in our environment: formaldehyde, terpenes, phthalates, benzene, naphthalene, pesticides, acetaldehyde, acrolein, propanal, butanal, benzaldehyde Isopentanal, pentanal, hexanal, etc. 

Microbiological pollutants

Indoor air can carry various microbiological pollutants:

  • allergens carried by pets, cockroaches, mites, plants (Ficus), etc.
  • micro-organisms such as bacteria, molds and their productions (microbial volatile organic compounds, toxins, etc.)
  • noncommunicable infectious germs (legionella in hot water tanks).

DID YOU KNOW? Moulds are microscopic fungi that can produce not only mycotoxins, but also volatile organic compounds of microbial origin (MVOCs) some of which can irritate the mucous membranes (eyes, nose). That “musty” or “earthy” smell so characteristic of damp, poorly ventilated buildings betrays the presence of MVOCs released by molds.

Physical pollutants

Buildings may contain asbestos and the ground in some regions may release radon (gas of natural origin, that is odorless and radioactive, in Belgium present mainly in schistose soils).

Indoor air pollution is influenced by several factors: 

  • the lack of fresh air intake and ventilation and the fact that the air is not renewed
  • damp that fosters the development of molds and microorganisms
  • lack of cleaning which encourages the accumulation of household dust, toxic substances from furniture, coatings and building materials, etc. 


In collaboration with the regions, Sciensano carries out sampling and analysis on a number of microbiological pollutants (bacteria, fungi, molds) in private (residential) and public places.

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