Keeping pee in encourages a sequence of events inside the body which can lead to bladder and kidney stones, bladder infections, heart and circulatory disorders and, for men, prostate enlargement.

Increased pressure in the bladder inhibits new urine entering, putting a back pressure on the kidneys. Raised pressure in the kidneys slows down their filtration of the blood, reducing the elimination of toxins from the body and disrupting the kidneys' control of water, salt and electrolyte levels. This can lead, for instance, to high blood pressure and heart disease.

The bladder itself responds to high pressure by expelling water through its lining, concentrating the (now saltier) urine. Crystals are more easily formed in the saltier urine, called bladder 'stones'. It is likely, but not yet certain, that concentrated urine also leads to kidney 'stones'. Sufferers are advised to drink more water to dissolve the stones, but the real solution is not to create a concentrated solution in the first place, by peeing regularly.

In men, pressure within the bladder not only increases the likelihood of bladder infections but also prostate problems. All urine passes through the prostate on the way to the penis but a full bladder presses down on the prostate, which resists by enlarging itself. Unfortunately, this squeezes the urethra (the urine passage), preventing complete bladder emptying leading to a need to pee frequently ...

Ed.- ... and sometimes incontinence and impotence.