When the pressure in your bladder builds to the point that it forces urine out through the urethra you have a condition known as overflow incontinence. This typically results in a steady dribble or stream of urine escaping and can be a very embarrassing experience.
So what creates the pressure in the bladder? Actually it's caused by the bladder not fully emptying itself causing a backup of urine and that backup exerts pressure. There are a number of reasons why the bladder fails to fully void itself.
In men the culprit can be the prostate gland. As men pass the age of 60 there is a 50/50 chance of developing BPH which is a benign growth of the gland. The urethra, the tube that runs from the bladder to the penis, runs through the center of the prostate. When the prostate enlarges it can pinch off the urethra causing weak stream, frequent urination and dribbling but also prevents the bladder from fully voiding itself. This of course means that the urine that is being sent by the kidneys to the bladder has no place to go and creates back pressure on the bladder.
Another cause can be that the urinary tract itself is being blocked. This can be from an infection or from small stones that occasionally are created. This condition is usually treated fairly rapidly by most individuals because of the discomfort associated with the infection or the passing of the stones.
Oddly enough constipation is also a cause of an over full bladder. If the rectum has hard stools lodged in it pressure will be applied to the bladder limiting its capacity. When the normal amount of urine hits the lowered capacity bladder there is an overflow and additional pressure to void the urine involuntarily.
Lastly overflow incontinence can be caused by diseases that affect the nervous system, spinal cord injuries and even medication. The best option is to visit your physician for a full examination to determine the root cause and then treat it.