Why does pee go yellow when we are dehydrated?

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Why does pee go yellow when we are dehydrated?

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Because it has less water in it. More water dilutes it and makes it appear clear because there is less of the non-water stuff in it that gives it its color relative to water.

Step 1: Put 1/2 cup of drink mix powder in a jar/glass.

Step 2: Add water.

Step 3: Observe.

Step 4: Add more water to the same glass.

Step 5: Observe once more.

Voilà.

Old red blood cells get broken down by white blood cells. One of the products of this breakdown is the chemical heme, which in turn is broken down, one of the products of which is urobilin. Urobilin is yellow and is eliminated by the body through urine, making it yellow.

When you’re dehydrated, your body is still eliminating waste products through urine, but there’s less water in the urine, making it more concentrated and darker coloured.

Your kidneys have a few different jobs. One is to work as a filtration device that removes certain molecules from the bloodstream. Another big on is to control how much fluid is in all of your blood vessels. It does this by reacting to (and adjusting) your blood pressure.

When you don’t have enough fluid in your blood vessels (dehydrated), your kidneys know to reuse as much of the filtration fluid as possible to ensure that the stuff that’s coursing through your veins is still in liquid form (bad news if it isn’t). When that happens, the water content of your urine is reabsorbed, leaving behind a kind of urine concentrate. The filtration has still happened and all those metabolites are still in your urine, but they exist in a much more concentrated form. On the other hand, when you have excess fluid in your vessels, the mechanics of the kidneys allow all that extra fluid to proceed on to the bladder. All that extra water content dilutes the urine and makes it clear.

Just wanted to add to the other answers that (pale) yellow is a **normal** color for urine to have, and does not mean you’re dehydrated. Urine is not supposed to be colorless, contrary to claims that tend to go around on the internet. Colorless urine means you’re overdoing it on the hydration, which isn’t healthy either. Not that you should worry if your urine is clear sometimes, but it shouldn’t be colorless most of the time, or you may start to experience symptoms associated with (mild) overhydration.

If your urine is a deep yellow, you may be a *little* dehydrated and should probably drink some water, but no need to worry (though you should generally try to keep it in the pale-yellow range). It’s not until you get into amber/rusty color territory that you’re really dehydrated and should drink fluids ASAP, and maybe replenish your electrolytes too. If your urine is very dark or brown, you may require medical attention for severe dehydration.