Asian Journal of Biology

Microplastics and nanoplastics are increasingly detected across environmental media and in human biological matrices, including blood, semen, and testicular tissue, raising concern about possible effects on male reproductive health. This review evaluates the principal mechanisms through which plastic particles may impair male reproductive function, their reported effects on semen quality, and the emerging human evidence. Experimental studies, particularly in rodents, indicate that exposure can induce oxidative stress, inflammation, endocrine and steroidogenic disruption, mitochondrial dysfunction, apoptosis, and impairment of the blood-testis barrier. These processes are associated with reductions in sperm count, motility and viability, abnormal sperm morphology, altered testosterone production, testicular injury, and disturbed spermatogenesis. Human studies provide evidence that microplastics can occur in semen and testicular tissue and suggest associations with selected semen-quality parameters. However, the human evidence remains limited by small study populations, predominantly cross-sectional designs, heterogeneous analytical methods, variable particle-detection limits, potential contamination, incomplete assessment of nanoplastics, and confounding by lifestyle and environmental exposures. Current findings therefore support biological plausibility but do not establish a causal relationship between microplastic exposure and male infertility. Future research should prioritise prospective human studies, standardised contamination-controlled methods, environmentally relevant exposure assessment, and integrated evaluation of particle burden, semen quality, reproductive hormones, and sperm DNA integrity.