Acute Air Pollutant Exposure and Cognitive Impairments in Healthy Young Adults: A Scoping Review of Human-Controlled Exposure Studies

Over the past decade, ambient air pollutant concentrations have increased, largely attributed to escalating energy consumption. Emerging evidence suggests that prolonged or repeated exposure to air pollutants may significantly accelerate the onset and progression of cognitive impairment, with studies reporting up to a 64% increase in systemic stress biomarkers and measurable cognitive deficits occurring within minutes of inhalation. Accordingly, this scoping review aimed to synthesize evidence from controlled human exposure studies investigating the relationship between acute air pollution exposure and neurological outcomes in healthy adults. To address this aim, eligible studies included literature examining exposure to airborne pollutants and assessing cognitive and neurobiological outcomes in human participants. A systematic search of PubMed was conducted using predefined MeSH terms and title/abstract keywords related to air pollution and cognition. Only full-text, English-language randomized clinical trials involving young adults were included. The study selection process was documented in accordance with the PRISMA guidelines, and methodological quality was assessed using the Joanna Briggs Institute (JBI) critical appraisal tool. Due to heterogeneity across studies, results were synthesized descriptively. Six clinical trials published between 2008 and 2024 met the inclusion criteria, with sample sizes ranging from 12 to 72 participants. Pollutants investigated included particulate matter, diesel exhaust, and elevated carbon dioxide concentrations. Across the included studies, these exposures were associated with impairments in executive function, attention, memory, and reaction time. Diesel exhaust exposure was associated with slower reaction times, while carbon dioxide inhalation increased working memory errors. Exposure to particulate matter was also associated with elevations in stress-related biomarkers. In contrast, filtered air conditions were associated with improved cognitive performance. Overall, acute exposure to air pollutants may produce measurable cognitive and neurobiological effects even in healthy adults, suggesting potential neurological vulnerability regardless of pre-existing conditions. However, the current evidence base remains limited. Future research should prioritize large-scale, ecologically valid studies to better define the mechanisms through which air pollutants disrupt neurological processes.