Around the time of a man's 25th birthday, his prostate begins to grow. This natural enlargement is called benign prostatic hyperplasia (BPH). It is the most common cause of prostate enlargement. Indeed, if a man lives long enough, he will almost certainly experience some degree of BPH. Keep in mind that this is a benign condition that doesn't lead to cancer, although the two problems can coexist.
No one knows exactly why BPH occurs. One popular theory suggests that the prostate begins to grow because of shifts in the balance between testosterone, a male hormone, and estrogen, a female hormone present in men in small amounts. Testosterone production declines with advancing age, changing the ratio of testosterone to estrogen. Some animal studies have shown that this shift in hormone balance may start a chain reaction, causing the rapid cell reproduction seen with prostate enlargement. Other animal studies suggest that the accumulation of the male hormone dihydrotestosterone (DHT) in the prostate may encourage cells to divide.
As the prostate enlarges, it starts to press against the urethra and the bladder, like a foot stepping on a garden hose or fingers pinching a soda straw. This gradually blocks the flow of urine, forcing the bladder to work harder to push urine through the urethra. But straining to urinate, although unavoidable, only makes matters worse. Like any muscle, the bladder wall becomes thicker with work. This reduces the amount of urine the bladder can hold and causes it to contract even when it contains only small amounts of urine, causing more frequent urination. Eventually, the bladder becomes so thick that it loses its elasticity and can no longer empty itself.
The course of BPH varies from one man to the next. In some, the disease may progress to a certain point and reach a plateau of mild symptoms that never worsen, or the prostate may continue to enlarge but grow away from the urethra, causing no additional impingement. Particularly in the early years of the condition, the symptoms may abate before worsening again. In other men, the disease progresses and the symptoms intensify steadily, year after year. In the worst cases, the prostate can grow as large as an orange.