Is it bad to hold your pee?

Humans should urinate 4-6 times a day. 

How do you know when you need to go? 

Inside the detruser muscles are millions of stretch receptors that trigger as your bladder fills. These send messages along the nerves to the spinal cord in the sacral region. A reflex signal travels back to your bladder making the detruser muscles contract slightly, increasing the bladder’s pressure making you aware it is filling up. At the same time the internal urethral sphincter muscle opens (the micturation reflex) - the brain can counteract it if it’s not a good time to urinate and send another signal to contract the internal urethral sphincter.  

You become aware of the bladder filling with approximately 150-200ml of urine in the bladder causing a stretch on the muscle wall. At 400-500ml the pressure becomes uncomfortable. Under normal circumstances your decision to urinate causes the external urethral sphincter to relax and the bladder to empty. The external urethral sphincter is part of the Pelvic Floor and provides support to the urethra and bladder neck. The pelvic floor muscles stop leakage from the bladder when we put pressure on the system by coughing, sneezing, laughing or jumping.  

Holding your pee for too long, forcing yourself to pee too fast, or urinating without proper support (eg. Crouching over the toilet seat) may over time weaken or over work the pelvic floor sling, causing pelvic pain, bladder pain, increased urgency or urinary incontinence. 

So, the odd urgent crossing of the legs on that long car journey we can cope with, but in the long run holding your pee for too long should be avoided!