High quality educational resources about semen are few and far between. I would venture to say that most of us learn about it either from self-experimentation, talking to friends or from porn. Semen is one of those taboo topics that carries a lot of cultural weight. Here’s a quick overview about how semen is made by the body, what it is made out of and how to tell if your semen is healthy.
What’s the difference between sperm and semen?
First things first, sperm and semen are completely different things. The terms are often used interchangeably but there are some important differences between the two. Semen is the fluid that comes out of the body during an ejaculation. Sperm are tiny cells that live inside the semen.
How are sperm made?
Sperm are created in the testicle when germ cells divide, grow tails and start swimming around. Sperm take about 72 day to mature and are stored inside the genital tract until they are ejaculated. In a normal ejaculate, there are usually millions of sperm cells swimming around in search of an egg to fertilize. Prior to ejaculation sperm cells are stored throughout the genital tract. Most of them are in a long-coiled tube on the backside of the testicle called the epididymis or at the very end of the vas deferens. The epididymis connects to the vas deferens which connects the testicle to the seminal vesicles and prostate where most of the seminal fluid is produced. During an ejaculation, sperm is joined with seminal fluid and pushed out of the body.
The purpose of semen
Semen, technically called seminal fluid, is specially designed by the body to protect, nurture and transport sperm cells on their journey into the female body to give them the best chance of fertilizing an egg. It is highly optimized to do this job perfectly. It contains key nutrients (such as zinc and vitamin C) that provide energy and protect sperm cells from getting damaged. It is thicker than most liquids and is designed to stick to the cervix to help sperm get as close to the egg as possible. It has a slightly alkaline pH and works to counteract the acid (hostile) vaginal secretions which can harm sperm. It is also full of proteins and hormones that send signals to the female immune system and reproductive tract that prime it for potential pregnancy. Like John Stockton, Magic Johnson or Russell Westbrook, semen is untouchable in the sheer number of assists that it provides to would be sperm on their journey to the egg. Sperm make babies. Semen provides all the support.
What is semen made of?
What is the magic formula to semen that makes it such a potent fertility fluid? Scientists have studied seminal fluid in depth and written up a list of ingredients and described the role of each.
Here are some of the headlines:
Sugar: Semen contains relatively high amounts of both fructose and glucose (2-5 mg per mL). Unlike other cells that have internal machinery to produce energy, sperm relies on the fluid around it for energy source allowing them to be leaner and swim faster. If it contains sugar, it must have calories, right? It does. Semen is has roughly 5 calories per mL or 10 – 30 calories per ejaculate.
Zinc: an element that is essential for DNA replication and is involved with many cellular functions. It is particularly important for healthy prostate function and the development of sperm cells. As such, semen has high amounts of zinc. Th e zinc level is about 135±40 micrograms/ml for healthy men. Zinc serves to help to stabilize the DNA-containing chromatin in the sperm cells.
Prostaglandins: proteins that act like hormones and have several functions in the body which range from inducing labor to helping individual cells grow. There are different types of prostaglandins present in semen which both nurture sperm directly and interact with the female reproductive tract to create a friendly environment for sperm cells and newly formed embryo.
PSA: a protein that is made by the prostate with the specific job of liquefying thick semen after ejaculation. Semen is naturally thick and coagulates following ejaculation to help it stick inside the woman’s body. It slowly liquefies over time releasing sperm into the cervix. PSA controls the liquefaction process. PSA is also used as a biomarker for prostate health.
Other things found in semen: Additional components of semen include salt, various proteins and amino acids, vitamin C and other antioxidants, calcium, magnesium, potassium, mucus, testosterone and other hormones. Semen can also carry bacteria and virus that cause sexually transmitted diseases including gonorrhea, syphilis, HIV, Zika Virus, HPV and others.
What part of the body makes semen?
Contrary to popular belief, semen is not made by the testicle. The testicles have two important jobs – they make sperm and they make testosterone – but they don’t make semen. The production of semen is mainly controlled by two small glands next to the prostate called the seminal vesicles which generate about 70% of seminal fluid. The remaining fluid mostly comes from the prostate (about 25%) and trace amounts from the testicle and the bulbourethral glands.
The Seminal Vesicles
Two small glands that sit atop the prostate are responsible for the lion’s share of seminal fluid. The size of these glands is influenced by testosterone levels which may be part of the reason that men with low T have lower semen volumes. Unlike their neighbor, the prostate, seminal vesicles rarely experience medical disorders.
The prostate gland plays an important role in male reproductive health. It is responsible for about 25% of seminal fluid adding key elements such as PSA and a bulk of the zinc. It is also responsible for controlling whether urine or semen pass out of the body. Can’t pee because you have a stiffy, you have your prostate to thank for that. As men age, problems with the prostate can cause issues with urination. It is also quite susceptible to developing cancer, so prostate cancer screenings generally start for men in their early 50s.
What is normal semen like?
Semen can change a bit in color, texture and volume from day to day and month to month. Most of these changes in semen quality are normal and can be influenced by frequency of ejaculation, diet, medications and drug use, testosterone level and a host of lifestyle factors.
Here’s a rundown of normal variations in semen quality:
Viscosity: Semen can be thick as toothpaste or watery. Typically, thick semen should liquefy over time (generally within an hour though sometimes it takes a bit longer) as PSA breaks down the coagulated proteins that cause semen to become viscous. Viscosity is influenced by frequency of ejaculation, diet, medications or chemical exposures and health of the prostate.
Color: Semen color can be transparent, white, grey or even yellowish. Color is determined by the relative contribution from each of the glands that make seminal fluid. It can also be influenced by diet and frequency of ejaculation.
Volume: A normal semen volume is 1.5 – 6.8 mL. Semen volume is most sensitive to frequency of ejaculation. Like sperm, seminal fluid is generated over time and it takes a day or two to fully recover fluid following an ejaculation. During long periods of abstinence, seminal fluid production slows or stops until ejaculation.
Healthy semen is a sign of a healthy man
Like sperm and a strong erection, healthy semen shows that all systems below the belt are in good working order. Signs that you could have a problem include consistently low semen volume, smelly, abnormally colored or consistently viscous semen. Also, if ejaculation is painful or if no semen comes out during orgasm, these issues are also worth a discussion with a urologist.
Mann, T (1954). “The Biochemistry of Semen”. London: Methuen & Co; New York: John Wiley & Sons.
Du Plessis SS1, Gokul S, Agarwal A. Semen hyperviscosity: causes, consequences, and cures. Front Biosci (Elite Ed). 2013 Jan 1;5:224-31.
Bygdeman M., Bendvold E., Gottlieb C., Svanborg K., Eneroth P. (1985) Prostaglandins in Human Seminal Fluid and Its Relation to Fertility. In: Bailey J.M. (eds) Prostaglandins, Leukotrienes, and Lipoxins. GWUMC Department of Biochemistry Annual Spring Symposia. Springer, Boston, MA
Bardin TP. The role of prostaglandins in reproductive physiology. Ohio State Med J. 1970 Oct;66(10):1008-12.
Isidori A, Conte D, Laguzzi G, Giovenco P, Dondero F. Role of seminal prostaglandins in male fertility. I. Relationship of prostaglandin E and 19-OH prostaglandin E with seminal parameters. J Endocrinol Invest. 1980 Jan-Mar;3(1):1-4.
Harvey, Clare (1948). “Relation between the Volume and Fructose Content of Human Semen”. Nature. 162 (4125): 812
Owen, D. H.; Katz, DF (2005). “A Review of the Physical and Chemical Properties of Human Semen and the Formulation of a Semen Simulant”. Journal of Andrology. 26 (4): 459–69.
Hampl R1, Kubátová J, Sobotka V, Heráček J. Steroids in semen, their role in spermatogenesis, and the possible impact of endocrine disruptors. Horm Mol Biol Clin Investig. 2013 Jun;13(1):1-5. doi: 10.1515/hmbci-2013-0003.
Adamopoulos DA, Lawrence DM, Swyer GI. Determinantion of testosterone concentration in semen of men with normal or subnormal sperm counts and after vasectomy. Acta Eur Fertil. 1976 Sep;7(3):219-25.
Kline EE1, Treat EG, Averna TA, Davis MS, Smith AY, Sillerud LO. Citrate concentrations in human seminal fluid and expressed prostatic fluid determined via 1H nuclear magnetic resonance spectroscopy outperform prostate specific antigen in prostate cancer detection. J Urol. 2006 Nov;176(5):2274-9.
Gonzales GF1, Kortebani G, Mazzolli AB. Leukocytospermia and function of the seminal vesicles on seminal quality. Fertil Steril. 1992 May;57(5):1058-65.
Abyholm T, Kofstad J, Molne K, Stray-Pedersen S. Seminal plasma fructose, zinc, magnesium and acid phosphatase in cases of male infertility. Int J Androl. 1981 Feb;4(1):75-81.
Mann T, Lutwak-Mann C. Evaluation of the functional state of male accessory glands by the analysis of seminal plasma. Andrologia. 1976;8(3):237-42.
Mann T. Secretory function of the prostate, seminal vesicle and other male accessory organs of reproduction. J Reprod Fertil. 1974 Mar;37(1):179-88.
Jung A1, Schuppe HC, Schill WB. Comparison of semen quality in older and younger men attending an andrology clinic. Andrologia. 2002 Apr;34(2):116-22.
Telisman S1, Cvitković P, Jurasović J, Pizent A, Gavella M, Rocić B. Semen quality and reproductive endocrine function in relation to biomarkers of lead, cadmium, zinc, and copper in men. Environ Health Perspect. 2000 Jan;108(1):45-53.
Gonzales GF1, Villena A. Influence of low corrected seminal fructose levels on sperm chromatin stability in semen from men attending an infertility service. Fertil Steril. 1997 Apr;67(4):763-8.
Bonnici J1, Fenech A1, Muscat C1, Calleja-Agius J2. The role of seminal fluid in infertility. Minerva Ginecol. 2017 Aug;69(4):390-401. doi: 10.23736/S0026-4784.17.04049-7. Epub 2017 Apr 10.
Robertson SA1, Sharkey DJ2. Seminal fluid and fertility in women. Fertil Steril. 2016 Sep 1;106(3):511-9. doi: 10.1016/j.fertnstert.2016.07.1101. Epub 2016 Jul 30.
Verze P1, Cai T2, Lorenzetti S3. The role of the prostate in male fertility, health and disease. Nat Rev Urol. 2016 Jul;13(7):379-86. doi: 10.1038/nrurol.2016.89. Epub 2016 Jun 1.
Bieniek JM1, Drabovich AP, Lo KC. Seminal biomarkers for the evaluation of male infertility. Asian J Androl. 2016 May-Jun;18(3):426-33. doi: 10.4103/1008-682X.175781.
Cui D1, Han G1, Shang Y1, Mu L1, Long Q1, Du Y1. The effect of chronic prostatitis on zinc concentration of prostatic fluid and seminal plasma: a systematic review and meta-analysis. Curr Med Res Opin. 2015;31(9):1763-9. doi: 10.1185/03007995.2015.1072707. Epub 2015 Aug 27.
Adefuye A1, Katz AA1, Sales KJ1. The regulation of inflammatory pathways and infectious disease of the cervix by seminal fluid. Patholog Res Int. 2014;2014:748740. doi: 10.1155/2014/748740. Epub 2014 Aug 11.