The prostate is a small gland that produces roughly 25% to 30% of the fluid in semen, helping sperm survive and reach an egg. It also plays a role in urinary control and ejaculation. About the size of a walnut and weighing around 25 to 30 grams, the prostate sits just below the bladder and in front of the rectum, wrapped around the tube that carries urine out of the body (the urethra).
Producing Fluid for Semen
The prostate’s primary job is making a thin, milky fluid that mixes with sperm and other secretions to form semen. This fluid contains zinc and citrate, among other compounds, which help nourish and protect sperm after ejaculation. Without it, sperm would have a much harder time surviving the acidic environment inside the vagina long enough to fertilize an egg.
The prostate also produces a protein that keeps semen in a gel-like state right after ejaculation, then gradually breaks that gel down so sperm can swim freely. This two-step process, first clumping and then liquefying, gives sperm time to be deposited close to the cervix before they’re released to move on their own. It’s a surprisingly precise bit of biological timing, and the prostate orchestrates most of it.
Controlling Urine Flow and Ejaculation
Because the prostate wraps around the urethra, its muscle fibers work closely with the sphincter muscles at the base of the bladder. These smooth muscle fibers contract around the internal opening of the urethra to help regulate when urine flows and when it doesn’t.
During ejaculation, this system does double duty. The sphincter near the top of the prostate clamps shut to prevent semen from traveling backward into the bladder, while the prostate’s own muscles contract to help push semen forward and out through the urethra. This coordination ensures urine and semen don’t mix, and that ejaculation has enough force behind it.
Its Connection to Erectile Function
The prostate itself doesn’t cause erections, but the nerves responsible for erectile function run right along its surface in two bundles, one on each side. These nerves signal blood vessels in the penis to relax and fill with blood. The prostate’s location makes these nerves vulnerable during prostate surgery, which is why preserving them is a major consideration during procedures like prostate removal for cancer.
When surgeons can spare both nerve bundles, roughly 67% to 75% of men recover erectile function within two to three years. When neither bundle is preserved, recovery rates drop to around 20% to 40% over the same period. Preoperative erectile health also matters: men who had strong erections before surgery tend to recover better afterward.
How the Prostate Changes With Age
A healthy prostate in a younger man is about the size of a walnut, around 25 grams. But the prostate never really stops growing. By the time a man reaches his 60s or 70s, it can swell to the size of a lemon, sometimes exceeding 80 grams, more than triple its original size.
This growth is called benign prostatic hyperplasia (BPH), and it’s extraordinarily common. About 50% of men show signs of it by age 60, and that number climbs to 90% by age 85. Because the prostate surrounds the urethra, an enlarged gland can squeeze the urine channel and cause a weak stream, frequent urination (especially at night), difficulty starting to urinate, or a feeling that the bladder never fully empties. BPH is not cancer and doesn’t increase cancer risk, but it can be a significant quality-of-life issue.
Common Prostate Problems
Prostatitis
Prostatitis is inflammation of the prostate, and it can affect men at any age, not just older men. There are four recognized types. The most common by far is chronic prostatitis, also called chronic pelvic pain syndrome, which causes pain lasting three months or longer in the area between the scrotum and anus, the lower abdomen, the lower back, or the genitals. Pain during or after ejaculation is another hallmark. The cause is often unclear, and it’s not always linked to infection.
Acute bacterial prostatitis comes on suddenly with fever, chills, severe pain, and difficulty urinating. Chronic bacterial prostatitis has similar symptoms but develops more gradually and tends to come and go. A fourth type, asymptomatic inflammatory prostatitis, causes no noticeable symptoms at all and is typically discovered incidentally during testing for something else.
Prostate Cancer
Prostate cancer is one of the most common cancers in men. Screening relies on a blood test that measures levels of that same protein the prostate produces to liquefy semen, known as PSA (prostate-specific antigen). When prostate cells grow abnormally, PSA levels in the blood tend to rise, though noncancerous conditions like BPH and prostatitis can also elevate it.
Current guidelines from the U.S. Preventive Services Task Force recommend that men aged 55 to 69 make an individual decision about PSA screening after discussing potential benefits and harms with a clinician. Screening is not recommended for men 70 and older. For men at higher risk, including Black men and those with a family history of prostate cancer, the evidence on whether to start screening before age 55 remains unclear, and no separate formal recommendation exists for these groups.
Why the Prostate Matters Beyond Reproduction
Many people think of the prostate as purely a reproductive organ, and its fluid-producing role is certainly its defining function. But its position in the body makes it a bottleneck for the entire urinary system. A healthy prostate keeps urine flowing freely, supports normal sexual function through its nerve connections, and coordinates the mechanics of ejaculation. When something goes wrong with the prostate, whether from normal aging, infection, or cancer, the effects ripple into urination, sexual health, and overall comfort in ways that can dominate daily life. That central role is why prostate health becomes increasingly important to pay attention to as men get older.