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Why Does Scuba Diving Make You Need to Pee in Your Wetsuit?

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A scuba diver pees underwater while exploring a tropical reef.

It is normal to feel the need to pee in your wetsuit when scuba diving.

istockphoto.com, RichCarey
I'll admit it -- I pee in my wetsuit! I simply can't resist the urge to urinate while scuba diving. I usually pee after a few minutes of being in the water, and then periodically throughout the dive. Like me, most scuba divers feel the need to urinate in their wetsuits. What's wrong with us? Are we drinking too much water? Do we simply have no self control? No! The need to pee during scuba dives is a normal physiological reaction. But "hold it" for a moment! Before I can explain why divers feel the need to pee in their wetsuits, I must first explain some simple physiology.

My Overly Simplistic View of the Circulatory System:

The human body is full of blood. The volume of blood may increase or decrease with hydration and other factors. Thankfully, the body has various mechanisms in place to maintain a constant volume of blood at all times. This keeps you from exploding in an icky red mess when your blood volume begins to increase.

Getting to the Heart of the Matter:

How does the body sense an increase in volume of blood in circulation? When the volume of blood in the body increases, the extra blood flows through the veins to the heart. In the heart, the increased volume of blood causes the atria (chambers) of the heart to stretch. To lower the volume of blood in circulation, nerve sensors in the atria trigger a cascade of reactions which increase urine production in the kidneys. This removes fluid in circulation and reduces blood volume.

Cold Water Makes You Pee In Your Wetsuit:

One reason that divers feel the need to urinate in their wetsuits underwater is called cold water immersion diaresis. Don't panic about the complicated name. The concept is relatively simple.

When a person jumps into cool water, his body automatically attempts to minimize heat loss by shunting blood alway from his skin's surface and extremities and towards his warm body core and vital organs. This is part of a phenomenon known as the mammalian diving reflex.

Although the total volume of blood in the diver's body has not changed, the volume of blood in his body core (particularly his heart) has increased. This triggers the body's high blood volume management system, which mainly involves increasing the rate of urine production in the kidneys (diaresis) as discussed above.

The end result is that the diver pees in his wetsuit.

Weightlessness Makes You Pee in Your Wetsuit:

Weightlessness, or near weightlessness, also causes blood to shift towards the body's core. This headward fluid shift was first observed in astronauts, who had to pee more than they normally would while in space. Weightlessness, like cold water immersion diaresis, triggers the body's high blood volume management reactions which increase the production of urine.

Neutral buoyancy as experienced by scuba divers so accurately mimics the experience of weightlessness in space that it has been used both to train astronauts and to conduct experiments about the effects of weightlessness. And, like weightlessness, neutral buoyancy also triggers the increase of urine production and makes you need to pee.

How Can You Reduce the Urge to Pee In Your Wetsuit?:

Cold water immersion diaresis and the headward fluid shift caused by the perceived weightlessness of neutral buoyancy combine to significantly increase a diver's urine production. Eliminating either of these factors will reduce the need to pee underwater. Stay warm by using a thicker wetsuit, or stay warm and dry by using a drysuit. I have found that drysuits definitely reduce my need to pee underwater. However, no matter how warm or dry a diver is underwater, he will still be neutrally buoyant (hopefully) and urine production will still occur at a faster than average rate. This is why pee valves are popular among drysuit divers.

Drinking Less Water Will Not Reduce the Need to Pee Underwater:

On land, consuming large quantities of water will cause a person to urinate more frequently. A diver might assume, therefore, that consuming less water will reduce his need to pee. This is not the case. A diver's body will sense the increased volume of blood in his body core regardless of his hydration level. Dehydration will only predispose a diver to decompression sickness and cause his pee to be smellier and darker than normal -- all the worse when he does break down and pee in his wetsuit. Drinking less diuretic fluids, such as coffee, before diving will reduce (but not eliminate) a diver's need to urinate underwater.

The Need to Pee Underwater Is a Normal Reaction to the Dive Environment:

So don't be embarrassed by your urge to urinate while diving. What's my advice for comfortable diving? Buy your own wetsuit, hydrate yourself before diving so your urine doesn't smell bad, and pee as much as you like. Urine is sterile so you are not going to create a health hazard if you pee in your suit. Simply remember to wash your suit in fresh water after diving (and not in the same rinse tank as the regulators, please!) Everyone else is peeing in their suits, why should you miss out on all the fun?
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