Any seasoned diver will testify to desperately needing to pee at some point during their dive and upon surfacing. It is a common sight on dive boats around the globe, the post dive race to remove your tank and wetsuit as quickly as possible and get to the toilet ASAP, the immediate queue for the toilets post and the accompanying “gotta pee” dance. So why does this happen? Why do I need to pee so badly when I dive?
The human body is designed for an environment with gravity, which slows our circulation causing a fair portion of our blood to pool in our extremities on land – our arms and legs. When we move to a weightless environment like underwater (remember how light your equipment feels after your giant stride entry?), our regulatory systems become confused.
Underwater as the effects of gravity disappear, the blood returns to the diver’s core or chest area, tricking the body into believing that the blood volume is too high. The body actively works to reduce this core blood volume; the heart responds by signalling our kidneys to remove this excess fluid by producing urine and voila the need the pee!
A further phenomenon is also working on our body as we dive – immersion diuresis. When a diver enters the water (immersion) they start to cool, since even the tropical water temperatures here on Ko Phi Phi of 28-30 C are colder than normal human temperature of 37°C. The water temperature is also cooler than the air, and as we cool the blood vessels in the extremities narrow, and once again the blood moves from the limbs and skin to pool in the core. Our body reacts to this and we feel the need to pee yet again.
Even the act of leaving the sea and removing our wetsuits can lead to exposure to a small gust of wind across the skin, causing a sudden increase in blood pressure, and resulting in that desire to pee. Add to this the muscles finally relaxing as you exit the water and the demand to pee can reach quite powerful levels.
In essence everything is conspiring against us scuba divers 😉 and the need to pee when scuba diving or snorkeling is 100% normal.