Tracing Microplastics in the Human Body: From Detection to Disease Mechanisms.

Microplastics (MPs), defined as plastic particles < 5 mm diameter, have become a growing public health concern. First identified in the aquatic environment in 2004 and later in air samples in 2015, airborne MPs display wide variations in shape and size, with fibres being the most common. These physical characteristics, together with others such as median aerodynamic diameter, influence how deeply they penetrate and where they deposit within the respiratory tract. Recent studies have confirmed the presence of MPs in nasal lavage fluid, bronchoalveolar lavage fluid, sputum, pleural fluid and lung tissue samples, with higher concentrations observed in older individuals, smokers and those with occupational exposure. Multiple polymer types have been identified, most frequently polypropylene, polyethylene and polyester. Experimental models demonstrate that MPs can induce inflammation, oxidative stress, mitochondrial dysfunction, microbiota alterations, fibrosis and carcinogenic changes, with toxicity generally increasing as particle size decreases. Despite the growing evidence of plastic toxicity, only a limited number of studies have examined MPs' influence on the respiratory system, focusing mostly on polyester spheres, rather than fibres, which dominate real-world exposure. Current findings suggest MPs contribute to several pathophysiological processes and may play a role in respiratory disease. However, further research is needed to clarify the underlying mechanisms, long-term consequences and clinical relevance of these emerging pollutants.