Everyday the average human inhales 11,000 litres of indoor air, constantly exposing them to the risks of indoor air pollution. Indoor air pollution is the presence of dangerous pollutants in the air inside buildings such as homes, schools or workplaces. These pollutants could be toxic chemicals, dangerous gases or airborne dust particles, but most commonly originate from indoor daily chores. In fact, researchers found that globally 2.4 billion people are directly exposed to indoor air pollution from cooking and heating with polluting fuels. From worsening asthma to life threatening lung conditions, indoor air pollution poses an invisible threat to human health everyday. 

Where does indoor air pollution come from?

Indoor air pollution has many sources, and most of them are part of ordinary domestic life. Cooking is one of the most significant contributors — gas and electric hobs alike release carbon monoxide, formaldehyde, and fine particulate matter, especially at high heat. Cleaning products, aerosol sprays, paints, and new furniture all emit volatile organic compounds (VOCs) — a broad category of chemical gases that can linger in the air long after use. Mould and damp, common in poorly ventilated homes, release biological pollutants that trigger immune responses and respiratory symptoms.

Other sources are less visible still. Radon — a naturally occurring radioactive gas produced by uranium decay in soil and rock — can seep silently through building foundations and accumulate in basements. Carbon monoxide from poorly maintained or unvented gas appliances is odourless and colourless, making it impossible to detect without a dedicated monitor. Even household dust, harbouring dust mites, pet dander, and pollen, is a persistent source of airborne irritants that most people do not actively manage.

Common indoor air pollutants include: particulate matter (PM2.5), volatile organic compounds (VOCs), carbon monoxide (CO), nitrogen dioxide (NO2), radon, mould spores, formaldehyde, and tobacco smoke. Many of these have no detectable smell or colour. Meanwhile, high levels of carbon dioxide (CO2) can affect productivity and increase virus transmission.

Global consequences 

Indoor air pollution has silently woven its risks throughout everyday life compromising respiratory health and overall well-being. As you inhale, pollutants coat the lining of your airways and lungs trigger an immune response leading to irritation and inflammation. While short-term exposure to indoor air pollution can cause headaches and worsen asthma, long-term exposure has been linked to chronic obstructive pulmonary disease, cognitive decline, and other life threatening conditions such as lung cancer and heart disease. 

The cardiovascular impact is frequently overlooked. Fine particles from indoor pollutants can enter the bloodstream through the lungs, contributing to arterial inflammation, raised blood pressure, and increased risk of stroke and heart attack. Research from Harvard T.H. Chan School of Public Health has highlighted that most people do not make the connection between the air in their homes and their heart health — in part because the damage accumulates silently over years.

There is also growing evidence that long-term air pollution exposure affects the brain. Studies have linked chronic exposure to neurocognitive decline and an increased risk of conditions including Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Pollutants appear to degrade the brain's cellular structures over time, with effects that are particularly pronounced in adults over 50.

Despite its severe impact, indoor air pollution is often ignored due to hidden nature and limited public awareness. Consequently, many lives are lost to preventable exposure each year. In 2021 alone, an estimated 309,000 deaths among children under the age of five were attributed to household pollution. More broadly, Indoor air pollution has been linked to around 17.4 million deaths since 2021, while continuing to cause 3.2 million premature deaths annually, underscoring its profound global health burden. 

Who is most at risk?

Whilst indoor air pollution affects everyone, certain groups face a disproportionately higher burden. Children, pregnant women, the elderly, and those with pre-existing cardiovascular or respiratory conditions are all considered particularly vulnerable.

Children are especially susceptible because their lungs are still developing and their bodies take in more air relative to their body weight than adults. Studies have shown that pollutant exposure can disrupt lung development in foetuses and young children at levels that produce no measurable effect in adults. Emerging research also suggests links between early exposure to indoor air pollutants and impaired neurological development, increased risk of childhood asthma, and disruption to endocrine function.

For the elderly, the body's ability to eliminate chemical toxins diminishes with age, meaning that the same level of exposure carries a greater physiological burden. In pregnant women, indoor air pollution has been associated with adverse birth outcomes including preterm birth, low birth weight, and complications during the first trimester. The WHO notes that women and children — who tend to spend the most time in domestic environments — bear a disproportionately large share of the health burden from household air pollution globally.

What can you do?

On average people spend 90% of their time indoors, and yet 70% of households don’t use air purifiers. Air purifiers can be extremely helpful with improving indoor air quality by continuously capturing harmful airborne contaminants and fine particulate matter. 

Ventilation is one of the simplest and most effective interventions available. Opening windows regularly — particularly during and after cooking, cleaning, or using chemical products — helps dilute pollutant concentrations and bring in fresh air. Using extractor fans in kitchens and bathrooms, and ensuring that gas appliances are properly serviced and vented, can significantly reduce exposure to combustion byproducts.

Monitoring is equally important, because many of the most harmful pollutants are completely invisible. Without a sensor, there is no way to know whether CO2 levels are rising, whether VOC levels are elevated after cleaning, or whether particulate matter is accumulating during cooking. Awareness is the first step to action.

Working with companies like MedicAir, Butterfly Air, AirGradient and Healthy Air Technology, we are helping AirTrack users be better informed and empowered to take immediate, data-driven action to improve their indoor air quality and protect their well being.

If you're interested in learning more about the science of what we breathe, we’ve compiled research on air quality in our Evidence Bank. This resource builds directly on our previous collaborative article on indoor and outdoor air pollution which broke down how air pollution overall is the leading environmental health risk. 

Know your air. Download AirTrack. 

Mia Simons overseen by Lia Budnik

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