Benign prostatic hyperplasia (BPH) is a result of the natural growth of the prostate gland. The prostate undergoes two periods of growth during a man’s lifetime. Early in puberty, the prostate doubles in size. Beginning around age 25, the prostate gradually begins to grow again.

It is during this second growth period that the cells in the central part of the prostate begin to reproduce rapidly. When the prostate enlarges, the tissue (capsule) that surrounds it prevents it from expanding. This forces the prostate to grow inward, causing it to constrict the urethra (the canal that carries urine out of the body), thus restricting urine outflow. This may cause the bladder wall to thicken and to contract even when small amounts of urine are present, resulting in frequent urination. Over time, the bladder continues to weaken until it is unable to empty completely.  

All of these changes within the prostate and surrounding area trigger the symptoms associated with BPH.

Physicians are unclear as to why the prostate gradually enlarges as a man becomes older. However, a few theories have been suggested. For example, younger men produce large quantities of the hormone testosterone and much smaller quantities of the hormone estrogen. 

As men age, the amount of testosterone production decreases, resulting in a higher percentage of estrogen. One theory suggests that estrogen may promote cell growth in the prostate, causing it to increase in size.

Another theory suggests that a hormonal substance derived from testosterone called dihydrotestosterone (DHT) may be responsible for prostate growth. Other experts believe prostate growth is a result of “instructions” coded in the body that cause certain cells to become active later in life and signal other cells to grow.

The testicles may also be associated with prostate enlargement. It has been noted that men who have their testicles removed at a young age, such as during the treatment of testicular cancer, do not experience enlargement of the prostate.

However, age is the primary risk factor associated with BPH. Men rarely experience symptoms before age 40, but the condition affects up to half of all men in their 60s. Ninety percent of men who are age 80 or older have experienced prostate enlargement, according to the National Institutes of Health, but do not necessarily have symptoms.

A family history of BPH also increases a man’s risk of developing the condition. BPH is more common in North American and European men than in Asian men. BPH also appears to be more common in married men than in single men, although scientists have not found a link between sexual activity and incidence of prostate growth.

Several studies have indicated overweight or obese men are more prone to BPH. However, recent findings from the long-term Air Force Health Study found the condition to be more common in tall men but not the overweight. Some research has found high blood sugar (hyperglycemia) or diabetes to be risk factors for BPH.