A Comparative Review of Molecular Mechanisms of Male Reproductive Toxicity Induced by Di-n-Butyl Phthalate, Diethyl Phthalate, and Di (2-Ethylhexyl) Phthalate

Abstract Phthalates are ubiquitous environmental plasticizers with established endocrine-disrupting properties. Growing evidence implicates di-n-butyl phthalate (DBP), diethyl phthalate (DEP), and di(2-ethylhexyl) phthalate (DEHP) in male reproductive dysfunction; however, their comparative molecular mechanisms require integrated evaluation. This review synthesizes studies published between 2016 and 2026 examining mechanistic pathways of phthalate-induced male reproductive toxicity. Seventy-four studies, including in vivo animal experiments, in vitro cellular models, and human epidemiological investigations, met inclusion criteria. Across models, DBP and DEHP consistently reduced sperm count, motility, and viability, disrupted testicular histoarchitecture, and suppressed testosterone production, while DEP demonstrated comparatively weaker effects. Oxidative stress emerged as a central mechanism, characterized by increased reactive oxygen species, lipid peroxidation, antioxidant depletion, and mitochondrial dysfunction. These alterations were closely associated with activation of apoptotic pathways, including caspase signaling and Bax/Bcl-2 imbalance, leading to germ cell loss. Phthalates also downregulated key steroidogenic enzymes such as StAR, CYP11A1, CYP17A1, and 3β-HSD, interfered with androgen receptor and PPAR signaling, and disrupted hypothalamic–pituitary–gonadal axis regulation. Emerging transcriptomic and epigenetic evidence indicates persistent DNA methylation changes and altered gene expression patterns, suggesting potential long-term or transgenerational effects. Comparatively, DEHP demonstrated the highest reproductive toxicity, followed by DBP, with DEP exhibiting lower potency. The convergence of experimental and epidemiological findings supports a unified mechanistic framework in which oxidative stress, endocrine disruption, apoptosis, and epigenetic reprogramming collectively impair male reproductive health. These findings highlight the need for mechanistically informed risk assessment strategies that account for mixture exposure and cumulative biological effects.