World Health Organization Guidelines for Indoor Air Quality

The World Health Organization IAQ standards and guidelines outline a number of potentially hazardous organic and non-organic substances that can have adverse health effects in homes in large quantities or after long periods of exposure. The WHO have identified three main groups of indoor pollutants that are particularly damaging to our environmental health; biological indoor pollutants, such as dampness and mold, pollutant-specific originating from chemical pollution, and pollutants from the combustion of indoor fuels. An ideal way to keep track of such harmful organic and non-organic substances, such as carbon monoxide, is by installing an indoor air quality monitor, which can warn you when your health is at risk.

What the threshold limit values are for major indoor pollutants

Bad indoor air quality can originate from a number of sources which are present in homes, commercial buildings, and other places of work. According to the WHO, biological pollutants can come from hundreds of different types of bacteria, molds, and fungi when there is sufficient moisture in the atmosphere. Indoor chemical pollutants have more diverse origins and are present in our homes as VOCs emitted from products we purchase. The WHO have highlighted eight specific chemical pollutants that have a negative effect on our air quality by 50 experts:


  1. Benzene

    • Threshold limit value: 0.1 ppm

  2. Carbon monoxide (CO)

    • Threshold limit value: 35 ppm

  3. Formaldehyde

    • Threshold limit value: between 0.1 and 0.3 ppm

  4. Nitrogen dioxide (NO2)

    • Threshold limit value: 3 ppm

  5. Naphthalene

    • Threshold limit value: 10 ppm

  6. Polycyclic aromatic hydrocarbons (PAHs)

    • Threshold limit value: Can range depending on the chemical.

  7. Radon

    • Threshold limit value: No evidence of a threshold with no risk.

  8. Tetra- and tri-chloroethylene

    • Threshold limit value: between 25 and 100 ppm


Another dangerous group that should also be mentioned is PM2.5, which according to the WHO, has two threshold limit values, a 10 μg/m3 annual mean and a 25 μg/m3 24-hour mean.


It is worth noting that indoor air quality can also be affected by outside pollutants, such as sulfur dioxide, which are usually present in urban areas from road vehicle combustion. Additionally, the WHO has also highlighted exposure to second-hand smoke (SHS) as one of the most important and widespread sources of bad indoor air quality.

What effects can they have on our health?

As people spend a lot of time at home or work indoors considering the health risks of bad air quality is quite important. Exposure to bad indoor air quality can have can have particularly adverse effects on the respiratory health of the young and elderly, and those who suffer from cardiovascular and/or chronic respiratory diseases.


Indoor air contamination has been linked to a number of respiratory symptoms, such as those related to asthma, chronic obstructive pulmonary disease, and rhinitis, as well as  respiratory infections. To a lesser extent, there is also some evidence to suggest that exposure to indoor air contaminants also cause hypersensitivity pneumonitis and pulmonary tuberculosis.


Many of the VOCs that are frequently found in homes are also considered carcinogenic, such as Formaldehyde.

How can poor air quality be reduced?

Good ventilation is essential to clearing indoor air of dangerous contaminants. The simplest way people can limit their exposure to bad indoor air is by opening their windows, however, ventilation systems can also be utilized for cleaning the air as well. That said, ventilation can sometimes be less effective due to poor placement of ventilation points, low levels of air volume, high levels of recirculation, and/or lack of maintenance. Therefore it is important to adequately assess how effective a ventilation system is operating regularly. It is also worth noting that energy efficiency measures are known to have both positive and negative effects on air quality , mostly due to making buildings more air tight. Therefore it should not be assumed that energy efficient buildings provide people with cleaner air.


An ideal way to assess indoor air quality is by conducting an exposure assessment. It then becomes possible to estimate or measure the frequency and length of time people are exposed to a contaminant. By understanding how often we are around harmful contaminants and where they are located, it is possible to take measures to isolate the impact they have on people’s health.

Understanding the dangers of contaminated indoor air

Studying the WHO’s guidelines for indoor air quality can promote better living and working environments. Additionally, it is also beneficial for people to develop an understanding of the following:


  • The different characteristics of semi-volatile organic compounds (SVOCs), a subcategory of VOCs. Knowledge of this can inform people on how to improve their environmental health by knowing how to avoid them.