This is what causes your poor indoor air quality

The indoor air can be up to 100 times more polluted than the outdoor air, according to the US Environmental Protection Agency. On average, indoor contains 2 to 5 times more contaminants than the outdoor air.

But what are these pollutants, and why and how do they enter our homes?

Poor indoor air quality is caused by the release of hazardous compounds from products such as candles, paints, and cleaning products. Activities such as cooking, using the fireplace, and cleaning without sufficient ventilation also causes air pollution. Other sources of air pollutants can be the soil underneath the house or nearby traffic or industry.

Common indoor air pollutants

There are many compounds that reduce air quality and pose some kind of health risk. The health risk is dependent on several factors. These include the type of compound, the amount present in your air, your exposure to them, and your overall health.

The most common air pollutants found indoors are:

  • fine dust particles
  • carbon monoxide (CO)
  • CO2 (carbon dioxide)
  • radon gas
  • volatile organic compounds (VOCs)
  • formaldehyde
  • mold

Unfortunately, most air pollutants are not noticeable since they are odorless and colorless. Therefore, it is good to get to know how these compounds enter your air.

Image of streetart. Kid with a balloon wearing a facemask.
Photo by Fred Rivett on Unsplash

Fine dust

Fine dust particles are really small dust particles. They are especially harmful since they can more easily enter your lungs compared to regular dust. Fine dust is found all over the house.

Indoor fine dust has many causes, including cooking, lighting candles, smoking, and outdoor air (coming from car exhausts). Outdoor air continuously enters the house through natural and mechanical ventilation, as well as when you open doors and windows. However, outdoor air is almost always cleaner than indoor air.

Carbon monoxide (CO)

Carbon monoxide (CO) is a colorless odorless gas that is formed by incomplete burning of carbon-based fuels. Incomplete burning happens in all fires but also in (efficient) appliances.

The most common sources of carbon monoxide are central heating systems and kerosene and gas space heaters such as geysers and boilers. Other sources of CO are gas stoves and the fireplace. Additionally, CO can enter the house via leaking chimneys and vents. Tobacco smoke is another source of carbon monoxide.

CO2 (carbon dioxide)

Carbon dioxide (CO2) is an odorless, colorless gas that only causes health issues in relatively high concentrations. High CO2 levels are most common in poorly ventilated rooms with a lot of people. Since people breathe out CO2, it accumulates in the indoor air when there is insufficient airflow and ventilation. Other sources of CO2 are cooking and the fireplace. In some cases, the soil underneath your house can emit CO2. This is mainly the case near farmland and mining operations.

You can read all about CO2 in our article: What are healthy indoor CO2 levels?

Radon gas

In the United States, radon gas is the second leading cause of lung cancer. Radon is a radioactive gas that is released from the soil. It is prevalent in many parts of the world. You can read all about radon in our article: What is radon? (origin, health risk, and preventive measures).

Volatile organic compounds (VOCs)

Volatile organic compounds are mostly human-made chemicals that are emitted as a gas from solids or liquid. There are very many different VOCs and their effects can range from highly toxic to no known negative health effects. (source)

The most common sources of VOCs in are:

  • paint
  • cleaning products
  • deodorizers
  • dry cleaning fluids


Technically formaldehyde is a common VOC. However, I want to mention it separately because it is stated by the Environmental Protection Agency (EPA) to potentially cause cancer. It is a colorless, pungent-smelling gas and can be released from insulation and building materials such as composite wood. Other sources are:

  • cleaning products, fabric softeners and conditioners
  • carpeting
  • glues and resins
  • tobacco smoke
  • a type of insulation called urea-formaldehyde insulating foam (UFFI)

Mold growth

The spores of molds are always present in the air in very small quantities. They normally do not pose any health hazards. However, when mold spores land in a spot that is humid and warm, they can start to grow and produce very high quantities of spores. This can lead to various health effects and can damage wood and fixtures.

The bathroom is the most common room with mold issues since they are often very wet and the air generally has a very high relative humidity.

Appliances and household products of concern

There are several common sources of indoor air pollutants that are present in almost every home or office. These appliances and products should be used with care and maintained properly in order to minimize their contribution to poor indoor air.

These products and appliances include:

  • carpets
  • cleaning products
  • poorly cleaned or maintained ventilation
  • geysers, boilers and central heating system
  • gas stove and fireplace
  • paint
  • candles and incense

Carpets and rugs

The relation between carpets and rugs and indoor air quality is an interesting one. Carpets and rugs trap dust particles that are kicked back into the air when you walk over them. Hereby, they contribute to a continuous circulation of airborne dust.

However, since carpets and rugs trap dust particles, they can be a dust sink when vacuumed regularly. Hereby, they can potentially contribute to the removal of airborne dust.

Additionally, carpets and rugs can themselves be a source of hazardous compounds since they wear out every time you walk on them.

If you are considering purchasing a rug, or already have a carpet or rug and want to replace it, I recommend to consider buying a natural rug that does not contain hazardous substances.

Natural rugs

I found a company called Natural Area Rugs that sells rugs made from all-natural materials such as jute, sisal, and even seagrass. These rugs really look amazing and do not emit any VOCs. You can find these wonderful rugs on

Cleaning products

Surprisingly, cleaning agents are a source of air pollution. Exposure to compounds emitted from cleaning agents depends on many factors, including its composition and reactive chemistry. It is safest to use natural cleaning agents.

Poorly cleaned or maintained ventilation

Ventilation is the most important factor for indoor air quality. Proper ventilation makes sure stale and polluted indoor air is transported outside and fresh outdoor air enters the room.

Is it strongly recommended to make sure you ventilate constantly and sufficiently. Therefore, you need to make sure that your ventilation system is regularly maintained and cleaned.

A general rule for the ventilation system is to clean it every three months and replace the filters twice a year. This, of course, depends highly on for example if you have pets or allergies (in that case you should replace and clean more often).

Geysers, boilers and central heating system

Household heating systems are a source of concern mostly due to their emission of carbon monoxide (CO). CO is emitted even from the most efficient appliances. Therefore, it is recommended to hang a few carbon monoxide detectors in your house. Most commonly in the bedroom to protect you while you sleep. Depending on where the water heating system is situated, another CO detector should be installed.

Gas stove and fireplace

The gas stove and fireplace are both sources of carbon monoxide as well as fine dust particles. Proper ventilation and airing when using the fireplace or when you are cooking is highly recommended. Installing a carbon monoxide detector is another safety precaution.


Regular paint is a source of volatile organic compounds (VOCs). These compounds are emitted from paint during the drying process, therefore it is recommended to air and ventilate constantly during painting. Additionally, according to an extensive study on the release of VOCs during and after painting, it is recommended to at least not use the painted room for 14 days. Another option is to look for low-VOC paint.

Candles and incense

Candles and incense can unfortunately consist of and therefore emit all kinds of potentially harmful compounds. A common air pollutant coming from candles is particulate matter or fine dust.

Healthier options are vegetable-based candles, soy candles, or beeswax candles.


It won’t come as a surprise that you need to stop smoking. Smoking does not only damage your lungs but also negatively affects the people around you. If you can’t stop smoking but want to minimize the exposure of your family and friends, stop smoking indoors. Smoking emits CO2, fine dust, CO, and many more hazardous chemicals.

Symptoms of air pollution

Air pollution can lead to many adverse health effects. If you want to read more about the short and long term health effects of poor indoor air, please read my article: What symptoms are often linked to poor indoor air quality?