The prostate is located inside the male body, just below the bladder. The urethra, through which all urine passes, goes straight through the prostate. When the prostate grows, which it normally does when men get older, it squeezes the urethra, which can make urination difficult or even impossible.
By the age of 50, one in two males experiences prostate enlargement and by the age of 80, this figure reaches about 90%. Why men's prostates become enlarged is uncertain, but the known risk factors are age and functioning testes (testicles that still produce sperm and the male sex hormone testosterone).
About half of all men with enlarged prostates experience symptoms. The constricted urethra makes it hard to empty your bladder, or to resist the urge to urinate:
Trouble resisting the urge to urinate
Sometimes these emptying problems can lead to a complete stop of urine flow and urinary tract infections that are difficult to treat. The symptoms described above can also be due to other illnesses in the lower urinary system, so you should always consult your doctor before starting any treatment.
Because the urethra is being squeezed, your bladder needs to apply higher pressure to get the urine out. This leads to a thickening of the bladder walls, which makes it less flexible and less elastic. This in turn means that the bladder cannot pull itself together as well as it used to, so all the urine inside can't be squeezed out. Residual urine can be the breeding ground for bacteria that lead to urinary tract infections.