Vasectomy is a birth control method in which all or part of the vasa deferentia are surgically removed, thus sterilizing the patient. Vasectomy should not be confused with castration: vasectomy does not involve removal of the testicles and it affects neither the production of male sex hormones (mainly testosterone) nor their secretion into the bloodstream. Therefore sexual desire (libido) and the ability to have an erection and an orgasm with an ejaculation are not usually affected. Because the sperm itself makes up a very small proportion of an ejaculation, vasectomy does not significantly affect the volume, appearance, texture or flavor of the ejaculate. Similarly, in females, hormone production, libido, and the menstrual cycle are not affected by a tubal ligation.
When the vasectomy is complete, sperm can no longer exit the body through the penis. They are broken down and absorbed by the body. Much fluid content is absorbed by membranes in the epididymis, and much solid content is broken down by macrophages and re-absorbed via the blood stream. Sperm is matured in the epididymis for about a month once it leaves the testicles, and approximately 50% of the sperm produced never make it to ejaculation in a non-vasectomized man. After vasectomy, the membranes increase in size to absorb more fluid, and more macrophages are recruited to break down and re-absorb more of the solid content. Though much of the content that can no longer exit the body is reabsorbed by these macrophages, examination has shown that, over time, essentially every vasectomized man also experiences an epididymal blowout, which is the formation of a sperm granuloma in the epididymis, to relieve the high intra-luminal pressures in the delicate epididymal tubules.