What Is Semen Made Of?

What is semen made of? The answer might surprise you.

The first and most common misconception to address is that semen and sperm are not the same thing. While the two terms are sometimes discussed interchangeably, semen and sperm are different. Sperm are reproductive cells that live and travel inside semen. Semen is a mixture of fluids that contains sperm, but the majority of semen is composed of over 200 separate proteins, as well as vitamins and minerals, including vitamin C, calcium, chlorine, citric acid, fructose, lactic acid, magnesium, nitrogen, phosphorus, potassium, sodium, vitamin B12, and zinc. That’s a lot of stuff to pack into a few milliliters of fluid.

The reason why semen contains so many of these compounds is mainly to assist the sperm. The proteins, minerals, fatty acids and other compounds in the semen primarily help provide the sperm with the energy they need to move and enter an egg, and this includes the natural resistance of the egg to the sperm. Sperm that enters another reproduction system is considered a foreign substance, and so the body it enters will work to reject it. One element of semen, lipids called prostaglandins, help the sperm evade detection by the other body. But this is just one small part that is actually a complicated mixture of fluids produced by several different organs.

How semen is made

The production of semen begins with the production of sperm in the testes. Once the sperm is produced, it’s stored in the epididymis (a series of ducts behind the testes) and matures there for at least a day. From the epididymis, the sperm travels to the seminal vesicles, the prostate and the bulbourethral glands, picking up the different fluids that comprise semen along the way.

Though sperm is perhaps the most notorious, it only accounts for between 1-5% of semen. While that percentage may seem small, semen are microscopic, and even in such a small total percentage, there can still be hundreds of millions of sperm in one average ejaculation. The exact amount of sperm in each ejaculation depends on a variety of factors, such as age, weight, diet and exercise.

Most of what comprises semen (roughly 70%) comes from the next step in the production process, the seminal vesicles. The seminal vesicles are a pair of glands below the bladder. The vesicles produce a fluid that contains nutrients, such as ascorbic acid (also known as vitamin c), amino acids, phosphorus, potassium and more. These minerals, acids and proteins help keep the sperm healthy. Most of the fluid, however, is made up of fructose, a form of sugar. Sugar is fuel, and its purpose in semen is to provide sperm with the fuel they need to travel through the body.

The next step in the process is the prostate. The prostate gland is responsible for producing fluid that accounts for about 25% of semen. Similarly to the fluid produced by the seminal vesicles, this fluid is mostly made of of nutrients, such as citric acid, calcium, zinc, magnesium and acid phosphate. Zinc is the most abundant mineral in this fluid, as it’s responsible for stabilizing the sperm’s DNA. Zinc is also responsible for semen’s color and taste.

The prostate also contributes a protein in semen known as PSA. This protein is responsible for breaking semen down into a thinner liquid after ejaculation. Semen is naturally thick to help it better adhere to the cervix when ejaculation occurs inside a vagina. After the semen is released, PSA helps to liquify the seminal fluid over time, which releases the sperm.

These three elements (sperm and fluids from the seminal vesicles and prostate gland) make up most of semen, but there is one other fluid that is found in small amounts (typically no more than 1% of semen). This fluid comes from the bulbourethral glands, which are found near the base of the penis. These glands are responsible for producing the fluid commonly known as pre-cum. Pre-cum is produced as a result of sexual arousal, and this mucus is responsible for lubricating the head of the penis and eliminating leftover urine from the urethra in preparation for ejaculation.

In discussions regarding safer sex practices, it’s often noted that pre-cum does not contain sperm. This is technically true, as we’ve just explained. Pre-cum is a separate substance that does make up a small amount of semen, which contains sperm, but pre-cum itself does not contain sperm. However, because pre-cum travels through the same pathways as semen, it can pick up other elements that make up semen along the way, including sperm. The likelihood of viable sperm being mixed with pre-cum depends largely on how much time has passed since the most recent ejaculation. However, as a rule, it’s important to consider that pre-cum is not always sperm free and could present a pregnancy risk, and, regardless of whether sperm is present, pre-cum is still a sexual fluid that can carry sexually transmitted diseases and infections.

Practicing safer sex involves a variety of different ideas and practices such as getting regular STD testing. Now that you know what semen is made of and how it’s produced, you’re more informed, and that’s another important part of safer sex.