Following puberty, the prostate gland is about the size of a walnut for much of a man’s life. However, around the age of 40 or 50, the prostate often begins to enlarge, a process referred to as benign prostatic hypertrophy (BPH). The reason for this physiological change is not completely understood, but is believed to involve a number of factors, such as increased levels of the female sex hormone estradiol and greater production of dihydrotestosterone, a derivative of the male sex hormone testosterone. When the prostate enlarges to a significant extent, symptoms of the condition, which chiefly consist of urination problems caused by the pressure of the gland on the urethra, usually ensue.