Does Air Pollution Increase the Risk of Dementia?

Yes. Unfortunately, air pollution increases the risk of dementia.

Large population studies show a link between long-term exposure to polluted air and a higher incidence of dementia. This does not mean that every exposed person will develop dementia. However, the increased risk is clear.

Dementia and Alzheimer’s Disease

Dementia is a general term for a group of symptoms. These include declining memory, thinking, reasoning, and the ability to perform everyday activities.
A person may have changes associated with more than one type of dementia.

Alzheimer’s disease is the most common cause of dementia. It accounts for approximately 60–70% of all dementia cases.

Vascular dementia results from blood vessel damage and impaired blood supply to the brain.

What Do the Latest Studies Show About Air Pollution and Dementia?

A systematic review and meta-analysis published in The Lancet Planetary Health in 2025 included 51 studies and data from more than 29 million people.

The studies examined whether long-term exposure to air pollution increases the risk of dementia. They defined long-term exposure as a period of at least one year.

Which Air Pollutants May Increase the Risk of Dementia?

Researchers found a statistically significant association between dementia and three indicators of air pollution:

• PM2.5: Every additional 5 µg/m³ in average long-term exposure was associated with an approximately 8% higher relative risk of dementia.
• Nitrogen dioxide (NO₂): Every additional 10 µg/m³ was associated with an approximately 3% higher relative risk.
• Soot, or black carbon: Every additional 1 µg/m³ was associated with an approximately 13% higher relative risk.

These percentages refer to changes in relative risk, not absolute risk.

A person’s actual absolute risk depends on age, genetics, cardiovascular health, lifestyle, and other factors.

Exposure to PM2.5

PM2.5 refers to suspended particulate matter with an aerodynamic diameter of up to 2.5 micrometres. This fraction includes particles with different actual sizes, shapes, densities, chemical compositions, and origins.

A US cohort study published in JAMA Internal Medicine in 2023 followed 27,857 people over the age of 50 for an average of 10.2 years. Researchers found the most consistent association with new cases of dementia for PM2.5 from agriculture and wildfires. The study examined long-term exposure. It does not show that a single wildfire increases the risk of dementia.

SEE ALSO: 11 Questions and Answers: How Do PM2.5 Particles Affect Health?

PM2.5 and the Risk of Alzheimer’s Disease

A large US cohort study published in PLOS Medicine in 2026 included 27.8 million Medicare beneficiaries aged 65 and older. An increase of 3.8 µg/m³ in five-year average PM2.5 exposure was associated with an approximately 8.5% higher relative risk of a new Alzheimer’s disease diagnosis. The association was slightly stronger in people who had previously suffered a stroke.

How Can Air Pollution Increase the Risk of Dementia?

Scientists are still studying the mechanisms that could explain why air pollution increases the risk of dementia. Evidence points to several interconnected processes.

Systemic Inflammation

Particles that penetrate deep into the lungs can trigger inflammatory responses.Inflammatory signals can then affect blood vessels and the brain.

Oxidative Stress

Air pollutants can impair the body’s ability to neutralize reactive molecules. This can damage cell membranes, proteins, and DNA.

Blood Vessel Damage

Air pollution is associated with hypertension, atherosclerosis, heart disease, and stroke. These conditions can contribute to vascular brain damage and dementia.

Possible Direct Pathways to the Brain

Ultrafine particles and some components of air pollution can enter the bloodstream.

Air pollution most likely affects the body through several pathways at the same time. It can act through the lungs, blood vessels, and immune system. Under certain conditions, it may also directly affect nervous tissue.

SEE ALSO: PM2.5 Particles Affect the Heart and Cardiovascular System
SEE ALSO: Air Pollution Affects Our Brain

Can Cleaner Air Help Reduce the Risk of Dementia?

In July 2026, the World Health Organization (WHO) published the second edition of its guidelines for reducing the risk of cognitive decline and dementia. For the first time, WHO included specific recommendations for reducing exposure to air pollution.

One recommendation addresses household air pollution. The other addresses ambient air pollution, particularly PM2.5.

A US study of 2,239 women aged 74 to 92 also points to the potential benefits of cleaner air. None of the participants had dementia at the beginning of the study. Over the preceding decade, a reduction in PM2.5 of 1.78 µg/m³ or in nitrogen dioxide of 3.91 ppb was associated with an approximately 20% lower relative risk of dementia. The median follow-up period was 6.1 years.

The study was observational. It therefore does not prove that improved air quality alone caused the lower risk. However, it shows that cleaner air may also be important later in life.

We Can Influence Our Own Exposure

Individuals have limited influence over outdoor air quality. However, we can reduce our exposure to some extent. We can monitor air quality and avoid spending time outdoors during periods of high pollution. But also, we can avoid strenuous outdoor exercise during these periods and choose routes away from busy roads.

We have much more control over the air quality in our own homes. Our decisions largely determine the quality of the air we provide for ourselves and other members of our household.

According to the Harvard University Healthy Buildings Program, we spend an average of 65% of our lives at home. Indoor air quality is therefore an important part of our total exposure. It is also something we can directly influence.

General Recommendations

The first step is to reduce the air pollution generated indoors.

Recommendations include:

• avoid cooking over an open flame whenever possible;
• limit the use of candles, incense, and other combustion sources;
• effectively extract pollutants generated during cooking;
• choose materials and products with lower pollutant emissions;
• do not smoke indoors;
• maintain good household hygiene;
• provide adequate ventilation;
• monitor PM2.5 and carbon dioxide (CO₂) concentrations;
• regularly maintain ventilation systems and replace filters.

A Local Air Purifier Is Not a Substitute for Ventilation

Local air purifiers can effectively reduce PM2.5 concentrations in a room if they have an appropriate filter and sufficient capacity. However, they do not supply fresh air. They therefore cannot reduce the carbon dioxide produced by occupants.

Air purifiers with standard particulate filters also do not remove gaseous pollutants such as nitrogen oxides (NOx) and sulfur oxides (SOx). Reducing these pollutants requires appropriate molecular filtration.

NOx and SOx can enter a building with outdoor air. Indoor combustion can also generate these pollutants.

Central Ventilation Systems Offer More Options

Compared with decentralized solutions, a central ventilation system usually offers more options for treating the air supplied to a building. More available space and higher available fan pressure allow the use of several filtration stages. These may include prefilters, fine particle filters, and molecular filters for specific gaseous pollutants.

The system treats the air before distributing it to individual rooms. At the same time, it can provide a controlled supply of fresh air, extract stale air, recover heat, and distribute air more evenly throughout the home.

Decentralized ventilation systems can be a good solution when there is no space for ductwork. However, limited space inside the unit and a smaller available filter area usually restrict the possibilities for multi-stage air treatment.

SEE ALSO: Mini Case Study: Verifying the Performance of a Central Ventilation System in an Apartment

Is a Central Ventilation System a Guaranteed Solution?

A central ventilation system does not provide these benefits automatically. Its performance depends on correct calculations, proper filter selection, available fan pressure, system airtightness, airflow balancing, and regular maintenance.

For this reason, the selection process should not start with the question: Which unit should I buy? Marquis Intelligence first analyzes the sources of pollution, outdoor air quality, how occupants use the space, and the existing technical conditions. Based on this analysis, we determine the required ventilation, particulate and molecular filtration, additional air treatment technologies, control strategy, and maintenance requirements.

The goal is not simply to purify air that is already inside the room. We need to provide enough fresh air and properly treat the air that we introduce into the home in a controlled way.

Clean Air Is a Good Foundation for a Healthier Life

Many factors contribute to dementia. Evidence shows that air pollution increases the risk of dementia. We cannot change our age or genetics. However, we can reduce our exposure to polluted air.

This does not mean that an air purifier, filter, or ventilation system can prevent dementia. Their role is to reduce our exposure to air pollutants and provide healthier conditions in the place where we spend most of our lives – our home.

References

1. World Health Organization. Dementia. Updated 3 July 2026. WHO.
2. Best Rogowski CB, Bredell C, Shi Y, et al. Long-term air pollution exposure and incident dementia: a systematic review and meta-analysis. The Lancet Planetary Health. 2025. DOI: 10.1016/S2542-5196(25)00118-4
3. Zhang B, Weuve J, Langa KM, et al. Comparison of Particulate Air Pollution From Different Emission Sources and Incident Dementia in the US. JAMA Internal Medicine. 2023;183(10):1080–1089. DOI: 10.1001/jamainternmed.2023.3300
4. Deng Y, Liu Y, Hao H, et al. The role of comorbidities in the associations between air pollution and Alzheimer’s disease: A national cohort study in the American Medicare population. PLOS Medicine. 2026;23(2):e1004912. DOI:10.1371/journal.pmed.1004912
5. World Health Organization. Risk reduction of cognitive decline and dementia: WHO guidelines, second edition. 2026. WHO
6. Wang X, Younan D, Millstein J, et al. Association of improved air quality with lower dementia risk in older women. Proceedings of the National Academy of Sciences. 2022;119(2):e2107833119. DOI: 10.1073/pnas.2107833119

 

This article is part of the “Air Pollution and Health” series, in which Marquis Intelligence, as a socially responsible company, highlights the adverse effects of air pollution on human health.

Document: MC-AP&H-015.26 – Does Air Pollution Increase the Risk of Dementia?