We spend up to 90% of our time indoors (offices, schools, hospitals, nurseries, shopping centers, and private homes). For this reason, the air quality that is breathed in them can affect the health of its inhabitants. 

Indoor air quality
Indoor air quality | Image Credit – iStock

According to the World Health Organization (WHO) groundwork, indoor air is 2–5 times more polluted than outdoors. WHO also states that in 2014, approximately 92% of the world’s population lived in regions where pollution control levels exceeded. 

The WHO has estimated the number of deaths globally attributable to indoor air pollution is 3.8 million annually. It has also classified this phenomenon as the tenth most important avoidable risk factor for the general population’s health.

Table of Contents

Sources of indoor air pollution

Sources of contamination in indoor air and their consequences on human health
Sources of contamination in indoor air and their consequences on human health | Image Credit – ResearchGate

At a milder level, pets share a home that can carry substances known as allergens. Additionally, they can block or damage ventilation systems designed to improve indoor air quality.

On the other hand, damaged or improperly installed appliances can produce harmful gases. Likewise, dampness or mold may arise due to poor installation of certain construction elements or different types of breakdowns. 

These humidities facilitate the proliferation of mites, fungi, and bacteria, which can cause respiratory diseases and asthma. We cannot stop talking about the conditions derived from the smoke given off, for example, by candles or tobacco (in case it is smoked inside the house).

The entry of external environmental pollution, such as polluting compounds that originate outside and leak into the indoor spaces, can also be harmful. We should note that some of these gases are also produced in homes through the domestic use of fossil fuels for heating and cooking.

Here are some common sources of indoor air pollution:

1. Ventilation deficiencies

Ventilation deficiencies
Ventilation deficiencies | Image Credit – ResearchGate

Ventilation provides air and must be sufficient to dilute pollutants to levels below human perception and those considered harmful to health. Ventilation may be deficient due to insufficient air volume, a high recirculation level, an incorrect location of the ventilation points, a poor distribution that leaves areas not ventilated, and a lack of maintenance or faulty design of the filter systems.

A study conducted in the United States that analyzed 97 buildings observed that poor maintenance of air conditioning systems was associated with increased respiratory, ocular, and skin symptoms among occupants.

It is very typical in developing nations to use fossil fuels to cool or heat the home and poor ventilation in the spaces where combustion occurs.

2. Exterior pollution

Exterior pollution
Exterior pollution | Image Credit – Imaggeo

Exterior pollutants enter indoor spaces from outside: Carbon Monoxide, hydrocarbons, and nitrogen oxides mainly from the combustion of motor vehicles, and sulfur oxides generated in power plants and other industrial processes.

Also, the external ozone formed as a secondary pollutant, and the contaminated inside air that goes outside can penetrate again through the air conditioning and ventilation systems.

Other contaminants seep through the building’s foundation (gasoline fumes, sewer fumes, and radon). It has been shown that when the concentration of a pollutant increases outdoors, it also increases indoors, although more slowly.

3. Chemical Pollution

Indoor Chemical Pollution
Indoor Chemical Pollution | Image Credit – NIST

The chemical pollutants in a residential building are combustion products with poor ventilation or poor maintenance: gas heaters, stoves, refrigerators, and ovens can release different pollutants.

Notable among them is Carbon Monoxide, a colorless and odorless gas produced by incomplete combustion of substances containing carbon. 

Sources are:

  • Typically kerosene-powered portable heaters
  • Wood-burning fireplaces
  • Furnaces
  • Dilapidated space heaters
  • Gas heaters
  • Car exhaust pipes
  • Second-hand smoke

Low concentrations can produce respiratory symptoms in healthy individuals and exacerbations in patients with chronic cardiopulmonary diseases. Although fossil fuels are replaced by cleaner energy sources in the modern world, 50% of all households globally and 90% of rural households continue to use fossil fuels as their primary energy source. It is women and children who are especially exposed to its effects.

4. Building materials and furniture

Newly decorated apartment
Newly decorated apartment | Image Credit – Flickr

Glass fibers used as thermal insulators in air conditioning systems quickly degrade and break down into particles that can be incorporated into air passages and reach lung tissue by inhalation. Also, asbestos used in construction and insulation materials can emit fibers into indoor air.

Although the World Health Organization has recommended not to use asbestos, it is the material still present in old buildings. It can be a source of contamination during maintenance and remodeling work and due to the degradation of materials that contain it. Room furniture and products used in cleaning and arts and crafts are formaldehyde, benzene, or toluene sources. 

Formaldehyde has been considered a human carcinogen, and its presence is common in plywood, panels, and chipboards used in the furniture industry. Formaldehyde is also used during the first months of aging of some varnishes to maintain the emission over time.

Benzene is a carcinogenic product whose primary sources are paints, resins, oils, plastics, detergents, and tobacco smoke. Office equipment (computers, printers, photocopiers) and office equipment (correction fluids, photographic solutions) are sources of harmful chemicals. Increasing the number of computers or other electrical devices in an office worsens the subjective feeling of air quality.

5. Human activities

Cleaning and personal hygiene products contain irritating respirable particles, although almost always in low concentrations. A study published in 2009 found a significant number of subjects with reactions to aromatic products: 19% had respiratory symptoms, headaches, and eye irritation. Also, insecticides and pesticides contain organophosphates or hydrocarbons that raise the concentration of volatile organic compounds.

6. Biological contamination

We can consider bacterial endotoxins, fungi, and dust mites as the primary biological contaminants. The levels of these pollutants are highly variable and change depending on weather conditions and cleanliness. 

The accumulation of organic material serves as a nutrient for fungi and bacteria, which is why wood, paper, paint, and carpets can harbor microorganisms. Poorly ventilated buildings promote microbial growth. Humidifiers that use recirculated water become contaminated and act as reservoirs. 

Without proper cleaning and disinfection of ventilation systems, occupants can be exposed to various biological agents, and the transmission of infectious diseases is also increased.

Indoor Air Issues

Indoor Air Issues
Indoor Air Issues | Image Credit – Burst

Did you know that nearly 1 in 12 school-age children have asthma? It is the primary reason for school absenteeism due to chronic illnesses. There is substantial proof that indoor environmental exposure to allergens (such as dust mites and fungi) triggers asthma symptoms. These allergens are prevalent in indoor spaces such as homes and schools. 

As for indoor air, problems do not always produce easily recognized impacts on one’s health, well-being, and performance. But they do exist, and they are essential. The most common symptoms include headaches, fatigue, shortness of breath, sinus congestion, coughing, sneezing, dizziness, nausea, eyes, nose, throat, and skin irritation.

Another consequence of poor quality air consumption is the drop in cognitive performance. Here are some indoor air issues that we should be aware of:

1. Immediate Effects

Some health effects may appear soon after a single exposure or repeated exposure to a pollutant. Such immediate effects are usually short-lived and treatable. 

Sometimes the treatment is simple: removing the person’s exposure to the pollution source if it can be identified. Soon after exposure to some indoor air contaminants, the symptoms of some diseases, such as asthma, may appear aggravated or worsened.

The appearance of immediate reactions to indoor air pollutants depends on several factors, including age and pre-existing medical conditions. 

In some cases, a person’s reaction to a contaminant depends on individual sensitivity, which differs tremendously from person to person. Some people can become sensitized to chemical or biological pollutants after repeated or high-level exposures.

Specific immediate effects are similar to those of colds or other viral illnesses, so it is often difficult to recognize whether symptoms result from exposure to indoor air pollution. For this reason, it is essential to pay attention to the time and place that symptoms occur. 

If symptoms disappear or subside when a person is away from the area, for example, an investigation is necessary to identify sources of contamination that could be possible causes. Some effects can be made worse due to inadequate renewal of outside air coming into the house or the prevailing indoor heating, cooling, or humid conditions.

2. Long Term Effects

Other health effects may appear years after exposure has occurred or only after long or repeated periods of exposure. These effects, including some respiratory illnesses, heart disease, and cancer, can be severely debilitating or fatal. It is wise to improve the indoor air quality in your home even if symptoms are not visible.

Although contaminants generally found in indoor air can cause many harmful effects, there is considerable uncertainty about what concentrations or exposure periods are needed to produce specific health problems. 

People also react very individually to exposure to indoor air pollutants. Additional investigation and research are needed to better comprehend the health effects after exposure to the average concentrations of contaminants found in homes and which occur at the highest concentrations for short periods.

3. Children Are More Susceptible

Children Are More Susceptible
Children Are More Susceptible | Image Credit – Flickr

It is known that children’s developing bodies may be more susceptible to environmental exposures than those of adults. 

Children breathe more, eat more food and drink more fluids in proportion to their body weight than adults. Therefore, indoor air quality is a more than genuine concern. Adequate indoor air quality maintenance encompasses safety, cognitive development, and the formation of critical and conscious beings.

4. Sick Building Syndrome

Sick Building Syndrome
Sick Building Syndrome | Image Credit – Freepik

All ventilation systems in poor condition can lead to problems for the user. But it may not be a direct consequence of our home or workplace, but something that is extended to the entire building. 

The WHO (World Health Organization) defined in 1982 what is known as “Sick Building Syndrome” (SBS) and involves the set of discomfort and illnesses that a building causes in its occupants and whose origin is in poor condition of the building. 

The symptoms to discover it, according to the National Institute of Safety and Hygiene at Work, are the following:

– Irritations of the eyes, nose, and throat

– Sensation of dryness in mucous membranes and skin

– Difficulty breathing

Erythemas (skin eruptions)

– Nonspecific hypersensitivities

– Nausea, dizziness, and vertigo

– Headache

– Mental fatigue

– High incidence of respiratory infections and colds

5. Poor Job Performance

According to survey data from the World Health Organization, 30% of workplaces have problems – in their indoor facilities – in terms of air quality. 

It can have direct consequences on the health of employees. Since it is not to be taken lightly to know that respiratory diseases are the leading cause of absences from work: from the flu to bronchitis -a consequence, for example, of pollution-, imply annual losses for employers due to the decrease in productivity.

Some pollutants up to five times more concentrated inside buildings than outside buildings have been detected. No matter where you are present, opening a window and letting in fresh air is almost always preferable to breathing the stagnant air inside.

6. Good indoor air quality makes you smarter

According to several reports, it may not be correct, but improving indoor air quality can increase productivity by about 10%. Other studies show that the results of school children can be improved by up to 13% if their class has an excellent indoor climate. So while fresh air can’t make you smarter, it will help you reach your full potential.

7. Indoor air can be up to 5 times more polluted than outdoor air

Much has been written about outdoor air pollution, and rightly so. Our environment should have the highest priority. However, we rarely talk about indoor pollution. Studies have shown that because of the chemicals, equipment, fabrics, and building materials used in our homes, indoor air can be 2 to 50 times more polluted than outdoor air.

8. We consume a lot of air

We know that what we place into our systems affects our body, good or bad. It is a clear trend that we are becoming more and more aware of what we drink and eat. But have you ever considered how much air you consume daily? The general rule is that we consume 1 kilogram of food, 3 kilograms of water, and 15 kilograms of air every day.

Simple Solutions to Bigger Problems

One of the solutions for indoor air pollution
One of the solutions for indoor air pollution | Image Credit – Wikimedia Commons

Maintaining indoor air quality was not a big topic in the past. But after the pandemic, when people were forced to spend most of their time indoors, the issue attracted much more attention. We can solve indoor air issues with simple habits and solutions without requiring a high technological installment. 

  1. Open your windows for 10 minutes a day. It allows you to renew the air in your home for free and effortlessly. And above all, it will enable you to reduce indoor pollution linked to various factors (dust mites, mold, humidity, etc.). It is essential not to ventilate for more than 10 minutes in winter to avoid the cold wall effect, promoting the appearance of mold.
  1. Leave the vents open: carbon monoxide (CO) is colorless, odorless, and fatal in high concentrations. This concerns heating or hot water production devices that are poorly maintained and operate in a confined atmosphere.
  1. Clean the pipes: infectious agents (bacteria such as legionella, viruses, toxins) come from the inhabitants of the accommodation (in the event of a contagious disease) or can develop in specific equipment (hot water production, dirty ventilation, air conditioning).
  1. Smoke outside: There are over 3,000 dangerous substances in tobacco. It is a proven source of pollution.
  1. Prefer synthetic materials that are washable at high temperatures and slatted bases for your bedding. Consider visiting the underside of cabinets and beds with your vacuum cleaner.
  1. Wash your curtains from time to time. Sofas made of leather or synthetic material are healthier in use than velour or fabric.


If indoor air quality was not a common topic in the past, the Covid-19 pandemic changed the situation, increasing the resonance of this issue. The measurement and control of indoor air quality through the implementation of filters and advanced air decontamination technologies are increasingly necessary and urgent in a world that is increasingly aware of the negative impacts of pollution on cognition. A world that will probably have to learn to live with the emergence of possible epidemics and pandemics.

(Last Updated on May 24, 2022 by Sadrish Dabadi)

Ankur Pradhan holds a bachelor’s degree in education and health and three years of content writing experience. Addicted to online creative writing, she puts some of what she feels inside her stormy heart on paper. She loves nature, so she is trying to motivate people to switch to alternative energy sources through her articles.