Causes of poor indoor air quality

Poor indoor air quality can affect your health. Learn about the causes of poor indoor air quality, such as indoor activities and sources, dampness and poor ventilation.

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Combustion-related activities and sources

Indoor combustion-related activities can contribute to poor indoor air quality by giving off particles or gases.

Key indoor activities that can generate indoor air pollutants include:

  • smoking
  • heating
  • activities that take place in an attached garage
  • cooking


Cigarette smoke emits a wide range of chemicals, such as:

  • carbon monoxide (CO)
  • formaldehyde
  • volatile organic chemicals (VOCs), including benzene and formaldehyde
  • particulate matter


CO, nitrogen dioxide (NO2), VOCs and particulate matter can be emitted from appliances like:

  • gas and wood fireplaces
  • gas or oil furnaces
  • gas water heaters

Activities that take place in an attached garage

An idling car, starting your gas-powered lawnmower or snowblower, operating a generator or using a barbeque inside your garage emits:

  • CO
  • NO2
  • VOCs
  • particulate matter

These pollutants can enter the home when the garage door is open or closed.


Cooking methods like frying emit more particles than others and can also increase humidity levels. Cooking with a gas stove increases the amount of pollutants if a range hood is not used properly. Pollutants include particulate matter and NO2.

Non-combustion sources

Household items, personal care products, building materials and hobbies can also contribute to poor indoor air quality.

Household items

Household items can release gases such as VOCs, including formaldehyde, into the air in your home. This is known as off-gassing. Some items can also produce particles. Items that can release gases or particles include:

  • furniture and cabinets
  • carpets
  • candles and incense
  • cleaning products

Carpets, fabric, foam chair cushions, pillows and mattresses can also attract dust mites. These mites produce allergens.

Photocopiers and some portable air cleaners may also produce ozone.

Personal care products

Some personal care products such as cosmetics and perfumes can release chemicals into the air.

Building materials

Building materials can also release gases such as formaldehyde and other VOCs into the air. These materials include:

  • insulation
  • flooring
  • wood products
  • glues
  • solvents
  • paints and varnishes

It is important to follow the manufacturer's instructions for installation and use.


Different hobbies can release gases and particles. Hobbies that can contribute to indoor air pollution include:

  • woodworking
  • carving
  • arts and crafts

Dampness and water leaks

Areas where stagnant water builds up or damp places like showers and basements are sources for biological pollutants like:

  • bacteria
  • mould and fungi

High humidity, leaks, water infiltration and flooding conditions can cause mould to grow indoors.

Poor ventilation

Poor indoor air quality is affected by the level of ventilation in a building, such as:

  • how much fresh air is entering the building from outside
  • how effectively contaminated air is being exhausted from the house

Good ventilation removes stale indoor air and reduces the amount of indoor air pollutants. It also helps to limit the buildup of indoor moisture, which can contribute to mould growth.

Ventilation increases the amount of outdoor air that comes indoors. The level of outdoor air pollution should be considered when ventilating your house.

If there are strong indoor sources and outdoor air pollution levels are low, you may need to increase the ventilation.

During periods of high levels of outdoor air pollution, take measures to reduce air entering the home from outside. These include:

  • closing the window
  • turning on the air conditioning
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