Air Pollution May Reshape Alzheimer’s-Vulnerable Brain Regions—But the Pattern Changes With Age
Common outdoor air pollutants may be associated with structural changes in brain regions that are particularly vulnerable to Alzheimer’s disease, according to a new observational study led by researchers at the USC Mark and Mary Stevens Neuroimaging and Informatics Institute at the Keck School of Medicine of USC. The research, published in NeuroToxicology, examined brain scans and residential air pollution estimates from 1,484 adults who had no dementia or history of stroke. The findings point to a complex relationship between environmental exposure and brain aging: among older women, greater exposure to fine particulate matter and nitrogen dioxide was associated with a thinner cerebral cortex, while younger men showed an unexpected association between higher pollution exposure and a thicker cortex in many of the same vulnerable regions.
The contrast is striking because cortical thinning is generally associated with normal aging and, when accelerated in specific areas, with neurodegenerative disease. The cerebral cortex is the brain’s folded outer layer, containing networks involved in memory, language, attention, decision-making and sensory processing. In Alzheimer’s disease, damage often emerges in a characteristic sequence that includes the entorhinal cortex, which serves as an important gateway for memory networks, followed by temporal and other cortical regions. In the new study, researchers focused on a composite measure encompassing the entorhinal, fusiform, inferior temporal and middle temporal cortices—areas known to be especially susceptible to Alzheimer’s-related changes.
The study combined data from two independent research groups that differed substantially in both age and sex. One group included 387 men from the Vietnam Era Twin Study of Aging, with an average age of about 62 years. The other consisted of 1,097 women participating in the Women’s Health Initiative Memory Study, whose average age was approximately 78. Using participants’ residential histories, the researchers estimated exposure to outdoor PM2.5 and NO2 during the three years preceding each person’s MRI scan. PM2.5 refers to airborne particles no larger than 2.5 micrometers in diameter—roughly one-thirtieth the width of a human hair. Because of their small size, these particles can penetrate deep into the lungs and may trigger systemic biological effects. Nitrogen dioxide is a reactive gas produced largely by fuel combustion, particularly from traffic and other urban sources.
Among the older women, higher exposure to both pollutants was associated with a thinner cortex across the Alzheimer’s-vulnerable regions. The researchers calculated that each additional microgram per cubic meter of PM2.5 exposure corresponded to an estimated cortical-thickness difference comparable to approximately 13 months of aging. For NO2, each additional part per billion was associated with a difference comparable to roughly three months of aging. These comparisons do not mean that pollution literally adds a fixed number of months to a person’s biological age, nor do they establish that exposure caused the tissue changes. Instead, they provide a way to express the size of the statistical association relative to typical age-related differences in cortical thickness.
The pollution signal was not limited to the four Alzheimer’s-related regions. In the older women, higher PM2.5 exposure was associated with a thinner cortex in 23 of the 34 brain regions examined, spanning the frontal, parietal, temporal and occipital lobes. Such a widespread pattern suggests that the effects of air pollution, if confirmed, may involve broad brain systems rather than a single memory circuit. Potential pathways include inflammation, oxidative stress, impaired blood-vessel function and disruption of the blood-brain barrier, a selective cellular interface that helps regulate which substances enter nervous tissue. Fine particles may also influence the brain indirectly through the lungs and bloodstream, although the present study did not measure the biological mechanisms responsible for the observed associations.
The younger men displayed a very different pattern. In this group, greater exposure to PM2.5 and NO2 was associated with a thicker cortex in the Alzheimer’s-vulnerable regions. While a thicker cortex is often interpreted as a sign of healthier brain tissue, that assumption is not always reliable. Some research suggests that cortical thickening can occur during early phases of certain disease processes, potentially reflecting inflammation, fluid-related swelling, enlargement of glial or neural cells, or other compensatory responses. Early pathological changes related to amyloid accumulation may also alter brain structure before later neurodegeneration produces measurable thinning. However, the study did not measure amyloid, tau, inflammation or other biomarkers, so none of these explanations can be confirmed.
An age-related analysis offered a possible clue to the divergent findings. Among the men, the positive association between PM2.5 exposure and cortical thickness gradually weakened between approximately ages 55 and 64 and became negative after around age 65. The later negative association was not statistically significant, meaning the evidence was insufficient to rule out the possibility that it resulted from chance. Even so, the trajectory raises the possibility that the brain’s structural response to pollution may change over the course of aging. A temporary thickening phase could represent an early biological reaction, followed by thinning as damage accumulates. This interpretation remains a hypothesis rather than a demonstrated sequence, because the participants were assessed at a single point in time rather than repeatedly over many years.
The researchers emphasize that the study cannot determine whether age, sex or other differences between the two groups explain the contrasting results. The participants came from separate cohorts with different demographic, health and life-history characteristics, and the analysis was observational. Residential pollution estimates also represent modeled exposure rather than direct personal measurements and may not capture time spent indoors, occupational exposure, indoor pollution, individual activity patterns or differences in pollutant composition. In addition, brain structure can be influenced by education, cardiovascular health, genetics, socioeconomic conditions, smoking, physical activity and many other factors. Statistical associations in MRI data therefore cannot be interpreted as proof that air pollution directly caused cortical injury or that the participants will develop Alzheimer’s disease.
Even with these limitations, the findings add to a growing body of research linking environmental exposures with brain aging and dementia-related biology. Air pollution is widespread, persistent and potentially modifiable through changes in transportation, energy production, urban planning and public-health policy. The study’s senior investigators argue that advanced neuroimaging can help identify possible effects of pollution years before dementia symptoms become visible. The next stage of research will require longitudinal studies that follow men and women from the same cohorts over time, repeatedly measure pollution exposure and brain structure, and include biomarkers for amyloid, tau, inflammation and vascular injury. Researchers will also need to track cognitive performance to determine whether pollution-related cortical changes predict memory decline or elevated Alzheimer’s risk. Until those studies are completed, the central message is one of caution: air pollution may leave a measurable imprint on the aging brain, but that imprint may not be uniform—and a thicker cortex at one stage of life may not necessarily signal better brain health.
Subject of Research: People
News Publication Date: 14-Jul-2026
Web References: https://ini.usc.edu/ ; https://keck.usc.edu/faculty-search/lauren-salminen/ ; https://doi.org/10.1016/j.neuro.2026.103495
References: NeuroToxicology, DOI: 10.1016/j.neuro.2026.103495
Image Credits: Stevens INI
Keywords: Air pollution, PM2.5, nitrogen dioxide, NO2, Alzheimer’s disease, cortical thickness, brain aging, neuroscience, environmental health, neurodegeneration
Tags: age-related brain changesAir pollution and brain agingAlzheimer’s disease risk factorscortical thinning and thickeningenvironmental neurotoxicitygender differences in brain responseneurodegenerative disease progressionneuroimaging biomarkersoutdoor air pollution health impactparticulate matter and nitrogen dioxide effectsUSC neuroimaging researchvulnerable brain regions in dementia
