Nicotine in cigarettes has a killing effect on sperm. Cigarettes contain a certain amount of harmful substances, and scientific research has shown that nicotine in cigarettes can break the double-stranded DNA of spermatozoa, making sperm development deformed and shortening the survival time, so cigarettes have a certain killing effect on spermatozoa. In addition, studies have found that the semen content of smokers is lower than that of non-smokers. This is because smoking affects the spermatogenic function of the testes, which decreases both the quantity and quality of sperm, and can aggravate the risk of fetal malformation. In view of the fact that cigarettes have a certain killing effect on sperm, men who are preparing for pregnancy can quit smoking in advance to improve the quality of sperm and reduce the risk of infertility or fetal malformation.