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Lee Bishop
Lee Bishop
Lee Bishop is a Ph.D. chemist (University of California-Berkeley, 2010), and is currently a postdoctoral researcher at the University of Wisconsin-Madison. He writes the general-audience science blog and contributes to the technical-audience chemistry blog




Posted in Science

"Why Is Pee Yellow?" or "Rainbow of Urine"

Oct. 26, 2011 9:34 am
Categories: None

This post originally appeared on

PeePee! Jokes about it will never stop being funny, and facts about it will never stop being interesting!

Do not try this at home. via phasezero

In this series of posts we will learn what pee is and discover how it connects us with the rest of life on earth and how humans have used it to learn more about the nature of the universe. Get ready for a wild ride!

To begin with, what is pee anyway? Well, like most things associated with life, it is mostly water (>95% in fact). The other primary constituents of pee are various nitrogen-containing chemicals (mainly urea for us and other mammals) that are the result of your body breaking down protein.

We will talk more about urea in future entries, but to start with let's talk pee color! The yellow color of your pee comes mostly from the breakdown of chemicals in your blood! Crazy right?!! Your body is constantly making new chemicals and breaking down old ones, and your blood chemicals are no exception.

The chemical in your blood that makes it red is called heme. Heme is the molecule to which oxygen molecules bind to be distributed throughout your body. The red color of heme is primarily due to electrons in its iron atom but also to electrons in its cool ringed structure (the ringed structure is called a porphyrin, and is found in plants' chlorophyll as well as in the ground's crude oil!). Your body turns the heme molecule from red to yellow by ejecting the iron atom out of the center and breaking the ringed molecule open using oxygen.

This is how your body gets rid of old heme molecules.

The ring-opened product is known as urobilin, and is one of the primary reasons your pee is yellow. Your pee tends to be more yellow in the morning than in the evening simply because there is a higher concentration of urobilin in morning pee since you've been breaking down old blood molecules all night.

Notice all the alternating single and double bonds (highlighted in blue) in both molecules and that metal (Fe = iron) in heme. Those are the two reasons they absorb visible light and are colored! This is a common theme for all colored molecules anywhere!

There are lots of jobs available in health care!

Any peepee aficionados out there may know that yellow is not the only color that your peepee can beebee. The pee of people who have a disorder called porphyria (derived from the greek porphyra, meaning "purple pigment") can be purple, brown, or even red! This is due to a malfunction in one of their enzymes responsible for manufacturing heme, which results in a log-jam of heme-molecule precursors that end up being urinated out.

Brownish urine can be caused by the buildup of porphyrin precursors. This peepee image and those below were taken from

Your pee can be intensely yellow- or orange-colored if you take excess B vitamins, specifically vitamins B2 and B12. Your body deals with this excess by just peeing them out. Notice how vitamin B12 looks similar to heme.

Look at all those alternating single and double bonds and that metal atom (Co = cobalt)! Chemistry is easy and fun!

Orange- or even red-colored urine can be caused by certain pharmaceutical drugs (e.g. rifampicin and phenazopyridine) or by beets (which contain cool betalain pigments such as betanin and indicaxanthin).

Orange urine can be caused by excess B vitamins, a variety of medications, and bunches of other stuff.

Perhaps best of all, the anti-malarial drug methylene blue (and lots of other drugs) can actually turn your urine green (blue drug + yellow pee = green crazy pee)!

Green urine can be caused by a variety of medications, or even foods such as asparagus.

I spoke too soon about the best pee of all. Purple (!!!) urine can result from bacteria smashing two light yellow molecules together to make the mega purple dye indigo. Incidentally, indigo was one of the first dyes ever produced by humans, dating back to 7th century BC Mesopotamia. It was produced in a nearly identical process to the one that happens in purple-peeing-people.

The bacterial transformation of indoxyl sulfate to indigo. Indigo changed the world, I'm not kidding, look it up.

Purple pee can be caused by the production of a mega famous dye by bacteria in your urine.

All these awesome colors are created by molecules that have either a single metal atom or alternating double and single bonds, which allows their electrons to move in such a way that they absorb visible light. It's that simple! When you pee the chemicals out they can make up less than 1% of your urine, yet they absorb so much light they can completely change the color of your pee!! Amazing!

Stay tuned for more PeePeePosts!
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