Semen is the fluid that carries sperm through the male reproductive system, into the female reproductive system, and toward the egg. Healthy semen is necessary for male fertility.
The majority of semen is “seminal plasma,” which contains fructose (sugar), enzymes, vitamins and minerals, and prostaglandins, a type of lipid (fatty acid) that helps sperm migrate from the vagina into the uterus. The fructose serves as the main source of fuel for the sperm, powering the movement of their tails as they swim to and penetrate the egg.
Semen also provides a “buffer,” protecting sperm from the acidic environment of the vagina by neutralizing those acids. The proper pH and nutrients are necessary for semen to provide its protection and fuel functions. Semen pH is tested as part of a semen analysis.
In a small number of people, semen contains the presence of antibodies that actually damage sperm, as a result of dysfunction of the immune system. These are known as “antisperm antibodies,” and they can lead to male-factor infertility.