The prostate gland surrounds the urethra just below the bladder. Starting around age 25, the prostate begins a second phase of growth that continues throughout a man's life. By age 60, more than half of all men have some degree of prostatic enlargement, and by age 85, that number exceeds 90%.
The growth is driven primarily by dihydrotestosterone (DHT), a hormone derived from testosterone. As the prostate expands, it compresses the urethra and creates resistance to urine flow. Over time, the bladder muscle thickens and becomes overactive as it works harder to push urine through the narrowed channel. This dual mechanism, prostatic obstruction combined with bladder overactivity, explains the wide range of BPH symptoms men experience.
