Why is Urine Yellow?

Peeing, a topic usually considered taboo, is a natural body function. Since it's something done multiple times a day, it has become a behavior that we may not think about much, but at one point or another I'm sure you've asked the question, why is pee yellow?

Urine gets its color from chemicals called urobilins. Urobilin is itself a product of bilirubins, bi-products in the breakdown of old blood cells (bilirubin also gives color to bruises and feces). The sequence is like this:

old blood cells -> bilirubins -> urobilins

When old blood cells break down in the body, the bilirubins travel through the blood stream until the liver siphons them out. From the liver, the bilirubins break down through the intestines and gall bladder and are expelled through the body in the feces.

Not all bilirubins get snagged by the liver, though. Those that remain in the blood stream are picked up by the kidneys; the kidneys break down the bilirubin into urobilin. The urobilin then exits the body in the urine, giving it that yellow tint.

The significance

You may notice that sometimes when you pee the tint of yellow will either be dark or light; this is a signal to whether or not you are well-hydrated. A hydrated person will have more available water in their body to get rid of. With more water the get rid of, the urobilins in the urine get diluted causing urine to have a lighter yellow color. And of course the opposite is also true. If a person is dehydrated, there is a lack of water in the urine; this makes the urobilin's presence more pronounced and the urine has a darker color.