90% Of Us Breathe Polluted Air. Is It Damaging Our Brains?

While it’s well-documented that air pollution affects our health, the problem is more severe than you might think. According to the World Health Organization (WHO), nine out of 10 people breathe highly polluted air, significantly impacting their health.¹ 

Outdoor pollution is the cause of 4.2 million deaths across the globe each year.¹ 

Indoor air pollution, which results from smoke, fuel, and unclean cookstoves, causes an estimated 3.8 million deaths worldwide.¹ Those deaths are attributable to both long-term exposure and short-term exposure. 

Pollution is also responsible for causing brain damage, respiratory issues, and cardiovascular events. As a result, we may even need to reconsider when, how, and where we exercise to attain full health benefits.

Burning fossil fuels is a primary cause of air pollution

John Walke, director of the Clean Air Project at the Natural Resource Defence Council, explains, "Most air pollution comes from energy use and production. Burning fossil fuels releases gases and chemicals into the air."²

According to the WHO, air pollution is “when an environment is contaminated by any chemical, physical, or biological agent that modifies the natural characteristics of the atmosphere.” 

The two most common types of air pollution are smog and soot.

  • Smog is a term derived from combining ‘smoke’ and ‘fog.’ It occurs when fossil fuel emissions react with sunlight. 

  • Soot is also known as fine particulate matter and consists of small particles of smoke, dust, soil, chemicals, and more.

Regardless of whether the air pollution exists as smog or soot, the source is usually the burning of fossil fuels. 

In urban areas, fossil fuel-related air pollution comes primarily from cars, trucks, power plants, and energy production. Forest fires also create fine particles that can enter the lungs.

Greenhouse gases (GHGs) like methane and carbon dioxide are also well-documented to have negative environmental and human health effects. 

Numerous air pollutants pose severe health risks and can even be fatal even in small amounts. 

Some of the most common forms of toxins that cause air pollution include mercury, lead, dioxins, and benzene.² In the US, approximately 200 such hazardous substances are regulated by the Environmental Protection Agency (EPA).

Air pollution is linked to worse brain health

Pollution affects human health in a variety of ways, but it most commonly impacts the lungs and heart. Some of the prevalent conditions resulting from air pollution include pneumonia, stroke, coronary artery disease (CAD), chronic obstructive pulmonary disease (COPD), and lung cancer.

Breathing polluted air can also have significant impacts on the brain. Many studies now show that living in polluted areas can result in cognitive decline. 

Cognitive decline is characterized by issues with memory, language, and decreased judgment or decision-making ability. 

Resources developed by the National Institutes of Health (NIH) describe that even mild cognitive impairment (MCI) can be a risk factor for dementia or Alzheimer’s disease.³ 

Environmental reports also indicate that inhaled pollutants can result in neuroinflammation (inflammation of brain tissue) and progressive neuron (nerve cell) damage.⁴ 

One large particulate exposure study of 19,000 female nurses between the age of 70–81 years old found that the women with long-term exposure to high levels of particulate matter (comparable to levels typically experienced by many people in the US) had a significantly worse cognitive decline.⁵

Additionally, more exposure led to a faster decline, suggesting a strong correlation between air pollution and reduced cognition. 

Another study with 680 male participants found being exposed to high levels of black carbon (associated with traffic-related air pollution) may have a negative effect on cognition in older men.⁶

Polluted air can cause developmental delays in children

For children, the impacts are significant as well. Research shows that pollution can negatively affect children’s cognition, including memory, attention, and intelligence. Moreover, the effects can start even before birth. 

One prenatal research study that followed children in New York City from before birth to the age of 6–7 found that those exposed to higher levels of air pollutants in utero (in the womb) were at a higher risk of experiencing attention problems, anxiety, and depression.⁷ 

A similar study which followed 200 children from birth to the age of 10, found that children exposed to higher levels of black carbon scored worse on memory and IQ tests.⁸ 

Air pollution is also linked to absenteeism at school and reduced academic performance.

One study at Michigan public schools located in areas with the highest industrial pollution levels found that those children had the lowest attendance rates and fewest students meeting testing standards.⁹ Though this study suggests an association between air quality and school performance, further research is needed.

In Mexico, a study comparing children from polluted and less polluted areas found that those exposed to urban pollution had more brain inflammation and damaged tissue.¹⁰ They also scored lower on memory, cognition, and intelligence tests than in rural areas. 

Air pollution may reduce the benefit of exercise

Exercise has well-known benefits for physical health. It’s also recognized to have positive effects on brain health. 

Much like other parts of the body, the brain requires circulation to receive nutrients and perform well, and since exercise increases blood flow, it can be very beneficial.¹¹ 

According to the Alzheimer’s Society, studies show that regular exercise can reduce the risk of developing dementia by 30%.¹² 

Unfortunately, the benefits of exercise on the brain appear negated by air pollution. A study with 8,000 participants found that while physical activity provides beneficial brain outcomes, pollution is associated with the opposite and may prevent the benefits.¹³  

According to Melissa Furlong, co-author of the research, "This study shows that air pollution is associated with worse brain health, including white matter lesions, which are linked with increased risk of stroke and neurodegenerative disease.” 

She also highlights that it’s not just severe air pollution that has an impact.

“This new analysis underscores the importance of re-evaluating emissions standards since even low levels of air pollution can affect the brain,” says Furlong.

How to lessen the effects of air pollution on your health

While pollution can significantly impact our health, there are ways to reduce its effects.

Avoid highways

Vehicle exhaust is among the most common air pollutants.¹⁴ Exposure to traffic-related pollution is linked to various health effects, including asthma, reduced lung function, and, as mentioned earlier, reduced cognitive function.¹⁵

If possible, avoid busy highways to reduce the impact of pollution on your health. If it’s an option, try to choose a place of work, housing, or school that isn’t right by a highway. 

When you venture outdoors, aim to walk in parks and other open spaces (where pollution levels tend to be lower). Trees naturally absorb air pollution, which reduces particulate levels.

Keep your home ventilated

Living in an area that isn’t heavily polluted may be challenging. For example, your home may be located near a busy freeway, or in a densely populated area. Moving may not be a current option.

In any home, good ventilation practices are vital. The United States Environmental Protection Agency (EPA) recommends keeping your home ventilated with clean air— whether that’s from outdoors when pollution levels are low or through an air filter.¹⁶ 

The EPA suggests having doors and windows closed during peak traffic times and using a filtration unit to keep the air clean indoors.¹⁵

Some air filters are more effective than others. While some simply recycle air, others filter out fine particles. Fortunately, the EPA provides guidance online to help consumers choose the right device to keep the air in their homes as clean as possible.¹⁶

Wear a mask

Wearing a mask is another useful tool to mitigate the effects of pollution. If you live in a busy urban area, or a highly polluted place, then wearing a mask can be helpful when heading outdoors. 

A study that measured mask effectiveness against wildfire pollution found that masks generally offered benefits.¹⁷ 

The study measured mask effectiveness by the number of hospitalizations attributed to smoke. While natural-fiber masks only offered minor reductions, N95 masks and surgical masks led to significant reductions in hospitalizations. 

The most effective masks can filter 95% of airborne particles to the size of 0.3 microns. These masks include N95 (United States), KN95 (China), and FFP2 (Europe).¹⁸

Check the air quality

Air conditions change day to day depending on the weather, time, and other factors. Checking local conditions and staying inside at peak pollution times can be helpful. 

If you’re based in the US, the Air Quality Index (AQI) can be found on AirNow.gov. The index ranks the air quality in your region. It’s a color-coded index for reporting the current air quality and forecasting the expected air quality. It is reported in real-time and updated every 2–3 hours.

Most countries have weather apps with local air quality rankings. 

If your regional air quality is low, it is advisable to wear a mask, avoid the outdoors, or use an air filter in your home.

Exercise strategically

While pollution may negate some of the positive brain benefits of exercising, keeping active is still very helpful for your general health. 

Deciding whether or not you should exercise when air quality is low can be decided on a daily basis.

According to the EPA, there are a few factors to consider, such as:

  • The air pollution level

  • Any underlying health conditions

  • The intensity and duration of the exercise¹⁹

If you have a pre-existing condition like a respiratory problem or cardiovascular disease, it may be best to avoid exercising in moderate or heavy pollution. Those who are without underlying conditions are considered safe to exercise on moderately polluted days.²⁰

For all people, being active outdoors when pollution levels are lower is helpful. Choosing parks, beaches, and open spaces (or well-ventilated indoor areas) are ideal. 

Does air pollution make mental health worse?

As well as impacting overall brain health, air pollution can also increase the risk of mental illness. 

One study found a correlation between living in industrial areas and poorer psychological health.²¹ Those who lived in areas with greater air pollution were found to have higher levels of anxiety and depression. 

A panel study with 12,615 urban dwellers in China found significant effects of air pollution on mental illness.²² Even a one-standard-deviation increase in air pollution concentrations (known as PM2.5 concentrations) per month, increased the risk of having a severe mental illness by 6.67%.

Further studies and research show that as concentrations of air pollutants increase, there is also an increase in 

  • Oxidative stress on the brain (antioxidant levels are low and free radicals are high)

  • Levels of depression

  • Depressive episodes leading to ER visits,²³ ²⁴

Both low-income and communities of color breathe disproportionately high pollution

It’s crucial to understand that both low-income countries and lower-income citizens are generally at a greater risk of adverse health impacts from air pollution. 

To this point, the Natural Resources Defense Council (NRDC) notes that historically, polluting highways and factories have often been built within communities of color, meaning that they are at increased risk of experiencing the harmful effects of air pollution². 

In 2019, the Union of Concerned Scientists found that communities of color in the Northeast and Mid-Atlantic breathe 66% more pollution than white communities.²⁵ Exposure to pollution for Latino residents was 75% higher and for Asian Americans, 73% higher than in white communities. At the same time, white residents make up 85% of people living in areas with the lowest pollution levels. 

Pollution also disproportionately affects those living in lower-income countries. According to the World Health Organization (WHO), over 90% of deaths caused by air pollution occur in low and middle-income countries–primarily in Asia and Africa, but also in the Eastern Mediterranean, Europe, and the Americas.

The lowdown

Air pollution can have wide-ranging effects on our health, including respiratory, heart, and brain health. With 90% of people living with air pollution levels above what the World Health Organization (WHO) considers safe, it’s essential to consider how pollution may be affecting you.  

If you are part of a higher risk group, living in or near an industrial or urban area, taking steps to reduce exposure is particularly important. 

While we can’t always control where we live, we can mitigate the effects of air pollution to protect our physical and mental health. A few tactics include avoiding densely polluted areas when possible, wearing a mask, checking the local air quality conditions, and getting strategic about how and when you exercise.

Also, consider contacting your local political representative to discuss areas of concern.

Finally, ask your family doctor about air pollution prevention measures for your health.

While we can’t always control where we live, we can take care to reduce the effects of air pollution on our physical and mental health.

  1. Air pollution | World Health Organization

  2. Air pollution: Everything you need to know (2021)

  3. What Is Mild Cognitive Impairment? | National Institute of Health

  4. Outdoor ambient air pollution and neurodegenerative diseases: The neuroinflammation hypothesis | Semantic Scholar

  5. Exposure to particulate air pollution and cognitive decline in older women (2012)

  6. Traffic-related air pollution and cognitive function in a cohort of older men (2011)

  7. Prenatal polycyclic aromatic hydrocarbon (PAH) exposure and child behavior at age 6-7 years (2012)

  8. Association of black carbon with cognition among children in a prospective birth cohort study (2007)

  9. Air pollution around schools is linked to poorer student health and academic performance (2011)

  10. The impact of environmental metals in young urbanites’ brains (2013)

  11. How exercise affects the brain | Life Science

  12. Physical exercise and dementia | Alzheimer's Society

  13. Association of air pollution and physical activity with brain volumes (2022)

  14. Vehicles, air pollution, and human health | Union of Concerned Scientist

  15. Best practices for reducing near-road pollution exposure at schools | Environmental Protection Agency

  16. Air cleaners and air filters in the home | Environmental Protection Agency

  17. Quantifying the health benefits of face masks and respirators to mitigate exposure to severe air pollution (2021)

  18. Air pollution masks: What works, what doesn’t | IQ Air

  19. Should you exercise outside in air pollution? | Environmental Protection Agency

  20. Living in grey areas: Industrial activity and psychological health (2011)

  21. Air pollution and mental health: Evidence from China | National Bureau of Economic Research

  22. Particulate matter, oxidative stress and neurotoxicity (2008)

  23. Effect of long-term exposure to air pollution on anxiety and depression in adults: A cross-sectional study (2017)

  24. Inequitable exposure to air pollution from vehicles in the northeast and Mid-Atlantic | Union of Concerned Scientist

  25. 9 out of 10 people worldwide breathe polluted air, but more countries are taking action | World Health Organization

Chloe Garnham is a writer exploring a broad range of topics, including healthcare, education, and technology.

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