Does long-term smoking in men actually have an effect on fertility? Some studies have shown that moderate or heavy smoking or long smoking may have adverse effects on male fertility. Smoking more than 20 cigarettes a day can affect semen volume, sperm concentration and sperm motility; long-term heavy smoking can lead to abnormalities in the interstitial cells and supporting cells of the testes, making the testes less capable of producing androgens. Harmful substances in cigarettes enter the blood circulation through absorption, and long-term accumulation leads to a gradual increase in the concentration of harmful substances in the blood circulation, which interferes with the microcirculation of the testes and epididymis and the exchange of substances in the internal environment, affecting the development process of spermatogenic cells and changing the biochemical conditions necessary for the maturation of sperm in the epididymis, resulting in a decrease in the number of sperm and reduced motility. Substances such as nicotine can directly affect spermatogenesis, and a nicotine concentration of ≥1 mmol/L can significantly reduce sperm motility. Heavy smoking can also alter testicular and epididymal hemodynamics and impede spermatogenesis and maturation. Nicotine is also a co-oxidant for biological samples such as sperm, and can reduce male fertility by inducing membrane damage, interfering with the glutathione (GSH) metabolic cycle, altering sperm morphology and viability, and inducing sperm DNA breakage. Smoke has teratogenic effects on sperm. Cd is present in cigarette smoke, and cadmium can cause sperm tail deformation and mitochondrial defects. Altered sperm morphology further affects sperm motility, thereby reducing male fertility. The risk of infertility is 2.4 times higher in couples in which either partner has a history of heavy smoking than in those without a history of smoking. The risk of infertility was 4.2 times higher if the history of smoking was greater than 5 years. In addition to affecting the semen parameters of adult men, smoking also has an impact on the fertility of male fetuses born in the womb. In a retrospective study of 1770 men, foreign scholars found that men with a history of prenatal smoke exposure had 20.1% lower sperm concentration than those without a history of smoke exposure, and that a history of prenatal smoke exposure also resulted in reduced sperm motility and smaller testicular size. If the mother smoked more than 10 cigarettes per day during pregnancy, the sperm concentration decreased by up to half compared to normal in men as adults and the risk of infertility increased significantly.