The prostate sits just below the bladder and in front of the rectum, and the urethra, the tube that carries urine and semen, runs straight through it. The ejaculatory ducts from the seminal vesicles open into the part of the urethra inside the prostate, so this is where the main ingredients of semen first meet.
Prostate fluid makes up about 25% of semen volume1. It is rich in zinc, citrate and a family of enzymes called kallikreins2. The best known of these is PSA (prostate-specific antigen, also called KLK3), the main enzyme that turns semen from a gel back into a liquid after ejaculation1. Small amounts of PSA leak into the blood, which is why a PSA blood test can be used to look for prostate problems.
The prostate matters for fertility as well as sex. Prostate disease or inflammation can affect how sperm function2, and some treatments for prostate problems can change ejaculation4. Researchers also think long-term prostate inflammation may play a part in prostate enlargement and cancer, although that link is still being worked out2.
What does the prostate do in ejaculation?
It adds a zinc- and enzyme-rich fluid that mixes with sperm and seminal vesicle fluid. Its enzymes then dissolve the semen gel so sperm can swim free.
At ejaculation, seminal vesicle fluid, prostate fluid and sperm-carrying fluid from the epididymis mix together and briefly form a coagulum, a soft clot that traps the sperm. PSA and related prostate enzymes break the clot down, and human semen usually liquefies within about 15 to 20 minutes1.
Zinc and citrate from the prostate are central to regulating this process and the wider cascade of events that ejaculation sets off2.
Does ejaculating more often protect the prostate?
Men who ejaculate more often have a lower rate of prostate cancer in large observational studies. That is an association, not proof that ejaculation itself is protective.
The biggest study followed 31,925 US health professionals from 1992 to 2010. Men reporting 21 or more ejaculations a month in their forties had about a 22% lower risk of prostate cancer than men reporting four to seven (hazard ratio 0.78), and the link was driven mainly by low-risk cancers3. Rates of PSA testing and biopsy were similar across the groups, and the results held in men who had been screened, so differences in testing do not explain it3.
Men who ejaculated more often also differed in other ways, including body mass index, physical activity and alcohol intake3. The researchers adjusted for these, but no observational study can rule out every other explanation. It is reassuring news, not a prescription.
How do prostate problems affect sex and semen?
Prostate inflammation can affect sperm function, and some prostate treatments change ejaculation. Urinary symptoms are the most common sign that something is going on.
Inflammation linked to infection in the prostate can impair sperm function and fertility2. Treatments for an enlarged prostate can also change ejaculation: alpha-blocker medicines and transurethral resection of the prostate (TURP) are both recognised causes of retrograde ejaculation4.
Talk to a doctor if you have trouble passing urine, need to go much more often, have pain in the pelvis or when you ejaculate, or notice blood in your urine or semen.
Common questions
Where is the prostate?
It sits just below the bladder, in front of the rectum, with the urethra running through the middle. A doctor can feel it with a gloved finger through the wall of the rectum.
Why is the prostate called the male G-spot?
Because it is sensitive, and some men find pressure on it, through the rectum, intensely pleasurable. If you want to explore it, go slowly, use plenty of lubricant and stop if anything hurts.
Does the prostate affect semen volume?
Yes. It supplies about a quarter of the fluid in semen. Some prostate treatments, such as TURP and alpha-blocker medicines, can reduce the amount that comes out by sending semen backwards into the bladder.
Read more on this
Sources
- Anamthathmakula P, Winuthayanon W. Mechanism of semen liquefaction and its potential for a novel non-hormonal contraception. Biol Reprod. 2020;103(2):411-426. PubMed
- Verze P, Cai T, Lorenzetti S. The role of the prostate in male fertility, health and disease. Nat Rev Urol. 2016;13(7):379-386. PubMed
- Rider JR, Wilson KM, Sinnott JA, et al. Ejaculation frequency and risk of prostate cancer: updated results with an additional decade of follow-up. Eur Urol. 2016;70(6):974-982. PubMed
- Parnham A, Serefoglu EC. Retrograde ejaculation, painful ejaculation and hematospermia. Transl Androl Urol. 2016;5(4):592-601. PubMed
Not medical advice. Written by Eric Stephens from the research cited above; not reviewed by a doctor. If something worries you, see a GP.