Evidence on microplastic exposure and respiratory health outcomes: a systematic review

BACKGROUND: Plastic fragmentation leads to widespread microplastic (MP) pollution. Inhalation of airborne MPs is a key human exposure route. Evidence links MPs to respiratory diseases, but causal mechanisms and real-world risks remain unclear. OBJECTIVES: This review synthesizes evidence on human exposure to airborne MPs and their role in major respiratory diseases. It aims to identify critical knowledge gaps and improve the framework for assessing inhalation health risks. DESIGN: This is a systematic review study. DATA SOURCES AND METHODS: PubMed, Scopus, and Web of Science were searched (up to 15 June 2025) using keywords for MPs and respiratory diseases. Two researchers independently screened articles, extracted data, and assessed the quality of the studies. RESULTS: A total of 17 studies were included. MPs are found in human lungs and can induce inflammation. Evidence associates chronic exposure with increased risks of COPD, asthma, and pulmonary fibrosis. A major limitation is that experimental animal studies use MP concentrations vastly exceeding environmental levels, limiting real-world risk extrapolation. Research is also disproportionately focused on polystyrene (PS), while occupational data implicate other polymers. CONCLUSION: Airborne MPs are a respiratory toxicant, but definitive causal evidence is constrained by a critical gap between experimental and environmentally relevant concentrations and a polymer-specific research bias. Future studies must prioritize environmentally relevant exposures, investigate high-risk polymers, and integrate exposomics with advanced toxicology.