Why does varicocele cause male infertility? Varicocele is one of the most common causes of male infertility, and according to statistics, 40% of men with infertility suffer from this condition. This disease can affect testicular function in several ways (1) When the veins become thicker, the mechanism that prevents blood from flowing backwards fails and blood that should have returned to the heart flows to the scrotum under the influence of gravity. (2) At the same time, some metabolic wastes in the veins, especially toxic substances from the kidneys, will accumulate and poison the testes, and when the varicose veins are stagnant on one side, these toxic wastes will also be transferred to the opposite side, so that the testes on the other side will also be damaged; (3) At the same time, the testes are intolerant of high temperature, and usually the temperature inside the scrotum is 1 to 2 degrees lower than that inside the abdominal cavity. Normally, the temperature inside the scrotum is 1-2 degrees cooler than inside the abdominal cavity, which is relatively cooler, but due to the stagnation of venous blood in the patient’s scrotum, the temperature increases, which also leads to a decrease in testicular function. The testes have two most important functions: synthesis of androgens and production of sperm. If androgen production decreases, this may indirectly cause sexual dysfunction; and a decrease in sperm production capacity may also affect the quality of the patient’s semen. Although it cannot be said that varicocele necessarily causes oligozoospermia, many of the patients with infertility due to decreased sperm concentration as well as motility suffer from varicocele. Therefore varicocele is likely to affect fertility and lead to infertility. The damage of varicocele to the testicles is very slow and if left untreated, it may be peaceful for many years, or it may go through ten or twenty years, for example, some patients in their fifties or sixties, whose testicles have been compressed by varicocele for many years, may experience testicular atrophy. It should also be noted here that azoospermia will not be caused by varicocele. Azoospermia is divided into obstructive azoospermia and non-obstructive azoospermia, etc. Obstructive azoospermia is caused by obstruction of the vas deferens, which is not related to varicocele, and the sperm of such patients is normal in most cases; non-obstructive azoospermia may be caused by various factors, and varicocele is not the main cause, but it can further aggravate the condition of azoospermia. Therefore, non-obstructive azoospermia may also be improved to some extent if varicocele is surgically treated.