Science Question from a Toddler: Why is poop brown?


Two Science Questions from a Toddler in the same month? It's a Festivus miracle! Or, you know, the unexpected byproduct of trying to write weekly blog posts during a month where damn-near all the sources you need to talk to are on vacation. But I'm a glass is half-full kind of woman.

Speaking of byproducts, BB reader Tammy says there's a small person in her life who wants to know, "Why is poop brown?"

First off, the fact that this kid's poop is brown is a really good sign. See, your stool can come in several different colors. Brown just happens to be the color of good health.

"Bile comes from your gall bladder and helps your body digest food," said Anish Sheth, M.D., assistant professor at Yale Medical School and author of the book What's Your Poo Telling You? "It's metabolized by the bacteria in your large intestine, leaving behind a byproduct called stercobilin—and it's that stercobilin that gives stool a brown pigment."

Without stercobilin, your poo would actually be a sort of pale, off-grey color, like white clay. This really does happen from time to time, Dr. Sheth said, when something is blocking a patient's bile duct, so that bile can't get from the gall bladder into the intestinal tract. The cause could be as simple as a gall stone, or as ominous as pancreatic cancer.

In fact, the color of poop can offer some surprising insights into what's going on with the human body. In the days before fancy medical technology, doctors looked at the color and texture of poop to help diagnose gastro-intestinal illness. Today, changes in stool are still frequently the first sign that something is wrong. There's three main "wrong colors" your poop can be:

While I had Dr. Sheth on the line, I decided that I had to ask him the ultimate "Why does my poop look like that" question. Oh yes, I asked about corn.

"There are a lot of things that we can't fully digest. I call it 'Deja Poo'. Corn is just the most common example," Dr. Sheth said.

The key is fiber. There's two kinds: Soluble and insoluble. If what you eat has a lot of insoluble fiber, it'll come out your other end mostly intact, because your body can't digest it. The foods that contain insoluble fiber foods are almost all plants, Dr. Sheth said, because humans haven't evolved the enzymes necessary to break down some plant cell walls. In the case of corn, some of the plant is soluble fiber and some isn't.

"There's two parts of the corn—the exterior kernel that we pass through and the germ inside of it. The germ is actually extracted. The whole kernel is immersed in digestive enzymes and your body pulls out what it can use," Dr. Sheth said. "What it can't use just passes on."

Ask Dr. Sheth your poop-related questions at his Web site, Dr. Stool

Image courtesy Flickr user GregtheBusker, via CC


  1. You can also get green poop by drinking too much of a blue liquid like blue Poweraid or Gateraid. I always assume it was the blue dye but maybe its somthing else.

  2. Green poop can also result from a particularly large black licorice binge. I once mailed an example studded with corn to a former landlord.

  3. Sufficient amounts of red wine can also produce that beet effect which I’ve heard referred to as “hangover black”.

  4. I like how the whole photo of the butterflies on the pile of shit fits with the mother and child aspect of the story. It’s a good photo, you can follow butterflies around all day with a camera and rarely find them feasting on a shitpile. Bravo.

  5. The first time I pooed after eating fresh roasted beets, I just about jumped out of my skull. It’s disconcerting to say the least.

    1. > The first time I pooed after eating
      > fresh roasted beets, I just about
      > jumped out of my skull.

      You mean you actually *look* at your poo after pooping? This is just sick and perverted !!!

  6. I ate a few blue-frosted cupcakes during Hannukah (more accurately pieces of cupcaked blue frosting — there was way more frosting than cake), and not only did it turn my poop bright green, it turned my urine bright green as well.

  7. I always thought it was like mixing all your paints together– you end up with brown most of the time.

    Note: if you drink a lot of blue Gatorade you will get green (or greenish) poop too.

  8. Certain (purple?) food dyes will break down to green.

    I am at present on an anti-inflammatory and it is really giving me the business in my stomach. Nothing like having to go have diarrhea every three hours.

  9. Green poop doesn’t necessarily mean a bacterial infection. Sometimes if digested food moves through your system too quickly for one reason or another, the bacteria doesn’t get to it, and it remains green. This can be caused simply by diarrhea or irritable bowel syndrome.

    I know this because my crap turned green about a month ago. Then I told her exactly what I thought of her. It was back to being brown the next day.

  10. I knew a guy who got hepatitis from drinking unfiltered water while training for a marathon in Okinawa. His poop was white, like a bar of soap, although I simply took his word for it. Some things you don’t need to see to believe.

    1. My dear Dad had white poop during a bout of hepatitis in Mexico in 1965. I wonder what the hep does to make this happen.

      1. White poo is known in the business as ‘clay colored stool’. In the case of hepatitis, bile isn’t making it through the liver.

  11. In Silence of the Lambs, Dr Lecter re-spells Dr Chilton’s name to C33 H36 ILTO6 N4, which is a re-hash of the chemical name for some of what causes poo to be brown. Or so I understand.
    Big insult, but if you only get insulted by Dr Lecter means you probably got off lightly.

  12. My son’s not a toddler any more (17 next week) but he’s still asking questions at breakfast that I can’t answer…this morning it was, “What happens to all the dead bacteria when milk is pasteurized? Are they still floating around in there? Or do they float up and make a scum they can filter off?” I suspect this has the potential to put him off milk altogether – sort of like when he found out about all the dead dust mites collecting in his pillow (age 7). We were saved then by a protective pillow case, but I don’t think they make them for milk cartons. Oh, dear…

    1. Haven’t you read Twilight? The best part of being a vampire: no poop, no pee. They just use up all their food (drink).

      1. Yeah, but if they happen to eat a bite of pizza while trying to get laid, they have to gag it back up.

  13. Hmm.

    In my experience, “Green” usually means “You drank a dark blue gatorade several hours ago”.

    Seriously, I don’t know what they color that stuff with… But it’s *powerful*.

  14. Those little packets of sugar free, grape flavored powder that you mix with water? One glass of that stuff, and I have green poop for two days. Awesome.

  15. Yeah, food colorings are soo much much fun. Go on a fruit-loops or apple jacks binge sometime, or drink a decent amount of grape soda and see how green things get.

    Or so I’ve heard.

  16. The worst situation I have encountered was when I was a kid a friend and I thought it would be cool to blow up electrolytic capacitors by over-volting them. neither of us thought about the consequences of inhaling the smoke. That next morning my poop was bright green, almost to the point of being a fluorescent color.

  17. I used to work in the cafeteria in college. One particularly slow breakfast shift, me and another guy decided to drink a LOT of grape Hi-C to see if it did, indeed, turn your poop green. It does.

  18. I read the article, and now know that brown is good. However, I still don’t know why poop is brown. I expected some explanation of the chemistry that makes it brown.

    1. You mean this bit?

      “[Bile is] metabolized by the bacteria in your large intestine, leaving behind a byproduct called stercobilin—and it’s that stercobilin that gives stool a brown pigment.”


      1. Re comments 32 and 32: That bit just says it’s brown because it’s brown. I’m with spgarbet.

    2. Saying it has stercobilin isn’t good enough? It’s tricky to explain why compounds have the colors they do.

      For some background, most organic pigments have many alternating single- and double-bonds. When these are all in roughly the same plane, the orbitals from the double-bonds can mix together. The more there are, the closer in energy the resulting molecular orbitals are. Eventually some gaps between them, which normally correspond to UV absorption, will come down into the visible range.

      The exact result, though, depends on a lot of things. Different parts of the molecule can attract or repel the orbitals, and sometimes symmetry makes energy levels line up. So while brown stercobilin, red phycoerythrin, green phycoverdin, and blue phycocyanin all have similar structures with lots of alternating bonds, the differences in color aren’t necessarily closely tied to any one part of their structure.

  19. I always thought (and though I don’t have it at hand, IIRC one of my sources is your guestblogger Paul Spinrad’s book on bodily functions) that the compound responsible for the brown is bilirubin. Do we have two names for the same compound here?

    1. Yep, my sources for The Re/Search Guide to Bodily Fluids said it was yellow bilirubin, which turns brown– so if bilirubin is a precursor to brown stercobilin, that all makes sense. Thanks!

      My follow-up question is: why is bird poop white on the outside and dark on the inside? And more mysteriously, why doesn’t it smell? (At least not very much.)

      1. Bird Poop is White on the outside & Black on the inside because they only have one hole, the Cloaca, & very effective kidneys: the White is from crystals of the Salts of Uric Acid in their Urine, and the Black is from the Feces.

  20. Now WE know Poop.

    If someone says we don’t know poop, we can tell ’em they’re full of poop!

    BTW, last July, I ate way too many of those red white and blue frosted animal cookies.
    My poop was the most intruguing shade of purple!

  21. !?

    I distinctly remember learning that the colour of poop depended on the amounts of bilirubin and billiverdin in your poo…one came from bile (the yellow billirubine?) and the green billiverdin came from I thought bacteria in the intestinal tract.

    Now I read that that is totally bogus?

    I GOTTA google this.


    OK…so billirubin does come from the gallbladder, as does billiverdin. They are also yellow and green, respectively. The latter is a result of the breaking down of part of hemoglobin. These two are responnsible for the yellow/brown colour of your poo. Apparently there’s much more at work, as the blurb above mentions, but at least I’m not totally mental and the two ‘ingredients’ I remembered aren’t totally bogus :)

  22. Bilirubun is the chemical Lecter encodes in the name, too. It’s a precursor of stercobilin, which is to say … same shit.

  23. So does that mean kool-aid is insoluble? Because I’ve always found that if you consume large amounts of it…well it basically does what those huge quantities of salt water are supposed to do when you’re doing one of those cleansing purges. Except much more colorful.

  24. Try drinking a few glasses of Welch’s Grape Juice. It starts out purple but it makes poo as green as Kermit the Frog.

  25. As previously mentioned, all of the bright multi-colored cereals. Fruity Pebbles can yield a bright green, almost like lime sherbet.

  26. Everything comes down to poo!
    Cardiovascular and lymphatic, yes, the nervous system, too!
    All across the nation, we trust in defecation!
    Everything comes down to poo!

  27. When I doing control system work at Wastewater Treatment Plants in the UK, there were a lot of wild tomato plants around. Lots of wasps too, feeding on the spiders, which fed on the flies.
    The Primary Settlement tanks were the best/worst. Big lumps sink to the bottom, chewing gum floats to the top. Don’t swallow or flush gum, kids.

  28. My wife picks blueberries for a commercial farm here during harvest time, so for two weeks or so at the end of the summer we have a diet that is high in blueberries.

    That first all-blueberry turd of the year is always a shocker. It looks like a bowlful of black coffee grounds. Magically, however, it smells like – blueberries!

  29. My wife is from Thailand and we eat a lot of Thai food… Chili peppers seem to be able to make the voyage intact much like the celebrated corn kernel.

  30. So it’s not typical to have a little blood in your poop? It’s usually after I eat something “spicy” which usually means Mexican food, so I’ve kinda figured it was somehow salsa or tomato related, and not a sign of my impending death.

  31. If Burger King ever brings back the Black Cherry slushie, your solid expulsions will be bright neon green. Scared the crap out of me (pun intended) but the first hit on my ‘green poop Burger King’ search found a very long thread of fellow sufferers.

  32. Among the 24 Stories of Filial Piety from 14th century China, one of them was the man who tasted his ill father’s poo to to gauge his father’s health. Bitter was supposedly good news, while sweet was very bad news. This act pretty much set an impossibly high bar for hundreds of generations of Chinese sons….

  33. A while back they were selling M&Ms in packs of single colours. The first time I took a dump after eating a pack of blue ones was startling to say the least.

    1. Anonymous #68–Look up “Bristol Stool Scale” on Wikipedia for a brief illustrated discussion of texture.

      When I report out from work with digestive problems, I always include a Bristol Stool Scale report for my boss: “Can’t come in today, I was up all night with diarrhea–this morning it’s a 6.5 on the Bristol Stool Scale!”

  34. Okay, okay, I get it. I just want to know one thing; what is going on with those butterflies in the picture? I’ll never be able to look at monarchs the same way…

  35. I remember the first time I realized what goes in effects what comes out… I had some Smurfberry Crunch (way back the first time the Smurfs were cool), and the next day my poo was a deep sort of aqua color.

    So, I guess normal poo color for Smurfs is aqua….

  36. I’m no dr. of scatology or anything, but I had my gallbladder removed several years ago, and by this explaination also the processes that make the brown-coloring bile and stercobilin. My poop has always remained brown. Sometimes it’s dark brown, sometimes it’s light brown, but it’s always brown. It’s not a pale gray color at all.

    1. Your gall bladder is just a storage tank for bile. It doesn’t produce it. After a cholecystectomy, your bile just goes from your liver to your bowel without the pitstop.

  37. Back when the Star Trek Experience was open in Vegas, I bought a six-pack of bright blue “Romulan Ale.” The beer was just OK, but the next day’s poo was gorgeous brilliant green! Panic changed quickly to delight, and I saved a couple of bottles to share with a friend and fellow trekker. Of course, I didn’t mention the side effect, but I made sure to foist the ale on him the day before St. Pat’s…

  38. Hey, this is Tammy, mom to the kiddo with the poop question. Thanks for answering our question! One down, eleven million to go…

  39. My friends and I refer to the “purple drink” phenomenon as “Ninja Turtle Poops”. I have had the occasion to experience a Leonardo-hued log after having a black grape Gatorade Slushie from 7-11. I think that they use mutagen-ooze to flavor that one. Someone should discover what it means to have a Donatello-colored dump. Now that’s science I can get behind!

  40. I had a bout of cryptosporidium a decade or so ago… and while that was running its course, I had white stool… that smelled frighteningly like peanut butter…. and so did my flatus. If it hadn’t been for the cramping and general malaise, it would have been funny.

  41. Green poo isn’t necessarily frmo bacterial infections. I’ve seen this when my kids were younger and ate breakfast cereals with LOTS of artificial colors/sweeteners. (i.e. generic Fruit Loops)

    Looked like they’d eaten a kelly green crayon.

  42. In Traditional Chinese Medicine (and probably Ayruveda) the color and consistency of your poop tells you a lot about what’s going on inside. For example, loose stool is a sign of a spleen deficiency.

  43. Actually, looking at the color of your baby’s poop tells you a lot about if he/she is eating enough or is sick:

    At first baby poop is dark brown/black, and if you’re breastfeeding the baby’s poop looks like yellow seedy mustard. It can even change color based on how mom’s milk changes from when the baby starts feeding to when it ends.

    Gross, yes, but quite useful when it’s 2AM and your sweet baby daughter projectile poops all over the bedroom curtains. :)

  44. How are we today?
    Better get a bucket, Im going to frow up.

    No, wait, that would just result in a spritely posting
    on the color of vomit.

  45. This is probably less pleasant, but can we talk about smell? Why does poop smell…like shit? Okay, the bacteria, but what bacteria, and why do they have to smell that way?

    Supposedly new borns who haven’t eaten solid food (thanks mom!) have neutral or even vaguely pleasant smelling poop. Can it smell different if you eat something in particular?

    Why do we cringe and curl up our noses at shit and urine soaked doorways, while dogs and other animals seem to find it fascinating, or a good read (smell)?

  46. so, this one time in china, I experienced some explosive liquid grey painty diarrhea with a weird chalky film over the froth. absolutely disgusting. I went to the hospital when it became clear after a week I wasn’t getting any better, and they gave me the most unsatisfying diagnosis ever: food poisoning. really? this was after both a blood test and stool sample, and the most specific answer I could get was “food poisoning.” I was too exhausted to pursue for further elaboration and spent the afternoon lying around with an iv, but I’m still, a year later, I’m totally perplexed by that illness. can food poisoning really result in whitish-grey paint poop? I accepted a beef dumpling when I learned they were out of goat. worst compromise ever.

  47. …Two points while we’re getting our shit together:

    1) I hate to bust the Dr’s shingle, but my gall bladder was blocked for what the biopsy showed was at least a decade, and both before and after its removal my fecal matter has always been a healthy shade of brown.

    2) Other colors also exist:

    * Blue: You’ve washed down an entire bag of Ruffles with at least a 20oz Blue Creme Nehi soda.

    * Purple and/or Some bright shade of Lime Green: Same as above, but with Grape Nehi instead. It’s believed Radar O’Reily experienced this quite frequently, with reconstituted Aaarmy mashed potatoes filling in for the Ruffles.

    * Bright Green: You’ve eaten a large bowl of Fruity Pebbles and/or Froot Loops, or you’ve washed down something with color to it with a bottle of Blue Creme Nehi.

    * Olive Drab: You’ve eaten a large bowl of Fruity Pebbles and/or Froot Loops with *chocolate* milk.

    * Runny, Light Brown with Gold Flecks: Your mother *told* you not to eat an entire bowl of Captain Crunch for a reason, kid!

    * Orange: You’ve devoured an entire bag of Cheetos. Note that in the early 70’s, this also applied to Quake’s Orange Quangaroos cereal, which was a side effect that helped kill sales almost as much as the fact that the stuff tasted like battery acid.

    …On a side note, from years of personal experience, I have not noticed my stools being reddened to any significant degree from ingesting Big Red soda, although one doctor advised me that reddish feces could be the result of blood, beets or Big Red. Go figure.

  48. Sometimes my Ball Python will poo that white, clay color that was mentioned. I wonder if it’s normal for a reptile or at least my species of snakes to do that.

  49. The Dr. is correct that the color comes from bile pigment. Your gallbladder is merely a storage tank for bile. It can be blocked at the cystic duct or even removed, and the bile which is made in the liver will still make it to the intestine. However, if your common bile duct is obstructed then your stool may lose color or become what is called “acholic”. You won’t care about it though since everyone will be commenting on how yellow your eyes look, and your urine will be dark tea-colored as the bile pigment finds other places to go. As far as stool is concerned, you can see any color, but as a general rule you don’t want to see black, white, or red. Food additives can cause this, but these colors should prompt investigation. Green isn’t necessarily an infection, but it can be-especially rotavirus, especially this time of year. Although having 20 explosive watery stools should be a clue, not the color. People worry way too much about the color of their stool.
    My biggest concern on seeing this article is why is this toddler pooping outside? Don’t they have indoor plumbing?

  50. I will simply state for the record that, as a toddler, my ingesting a large-sized Binney and Smith green crayon resulted in a panicked call to the pediatrician upon my next diaper change. Oddly enough, to this day, lime is my favorite candy flavor. ;D

  51. When I was a sewage treatment plant inspector I told my friends: “it might be shit to you, but it’s my bread and butter”.

  52. If it’s pink, then it’s 1971 and you’ve had WAY too much Frankenberry. The first iteration of Frankenberry cereal used a dye that had thousands of worried moms taking their kids to the doctor to find out why their kids’ poop was pink. Google “Frankenberry Stool” for details!

  53. My son (6 mo) had a poo not too long ago that smelled EXACTLY like movie-theater popcorn.

    My wife was changing the diaper; I wandered by, feeling inexplicably hungry…

  54. Regarding the composition of snake poo (posts 94, 96), the white, hard part of snake feces comes from the indigestible bones, fur, and other highly calcified tissues.

    I kept a friend’s burmese python for him while he was out of the country. The snake’s poo had two phases. First came a squishy brown pile, which made my wonder how the hell a rotweiler got into the snake’s cage. Then a couple days later he would produce a few hard, round, white balls. The actually bounced off the floor one day while I was holding him. Needless to say, the experience cured me of a desire to ever own a snake that big.


  55. The whole question of, why is poo brown?, leads to other questions and answers that cover the color of blood, urine, poop, and bruises. I remeber all my friends getting really excited the day we covered it in med school.

    But first, some people have asked a more physics-related question, which is: why is the molecule in poo perceived as a brown pigment? I’ll punt and just say that it’s because stercobillin absorbs all light, except those photons that contribute to the color we see as brown. That is because of the types of chemical bonds between the atoms that make up stercobillin – and the reason behind that is the subject of an entirely different thread.

    Now, the cool stuff about why the stercobillin gets there in the first place. It all starts with heme. Heme is a big molecule that is part of hemaglobin, the oxygen-carrying part of our red blood cells. Heme is red, and is the reason our blood looks red.

    Red blood cells are constantly being made and broken down. When the heme spills out, it is broken down to biliverdin, which is green. Biliverdin breaks down to bilirubin, which is yellow. People with liver failure have trouble breaking down bilirubin, and that is why they sometimes appear yellow, or jaundiced.

    As the article says, the bilirubin goes into the bile and breaks down in your GI tract to stercobilin, which is brown. At every step of this chemical process, the number and types of chemical bonds between the atoms in each molecule changes – and that’s why the color changes.

    You can watch this whole process in action the next time you get a bruise. A bruise is just a collection of blood under your skin that leaks out through tiny damaged blood vessels. Remember, the progression goes from heme (red), to biliverdin (green), to bilirubin (yellow), to stercobillin (brown). It naturally goes much faster in your GI system, but the same chemical changes happen right under your skin.

    You need to understand how colors blend together to really appreciate it, but you can watch a bruise start out very dark (lotsa red pigment), then as it spreads out you’ll see some greeen biliverdin around the edges, then later some yellow bilirubin when it really starts to spread out, and finally the bruise looks brown right before it goes away.

    Neat, huh? Science is cool.


  56. The “red” from beets is really not the same hue as blood — if you look at it, you’ll see that it’s purple.

  57. My brother once, in a fit of patriotism or something (actually he was high), he ate a whole bag of red-white-and-blue frosted animal cookies. Later that day he crapped purple. He took pictures before flushing.

  58. I just had to comment that both of the authors went to Brown University.

    That is all, thank you very much.

  59. Just have to report that eating a lot of chocolate biscuits can lead to a very deep brown colour, almost black, as I discovered this Christmas.

  60. A friend with a home juicer made carrot juice, the result was orange-ish poo.
    BTW carrot juice is damn tasty, but expensive to make as you need A LOT of carrots.

  61. Enough food dye will harmlessly stain a lot of your bodily fluids. This can be great fun when you know you’re going to be taking a urine test. Blue or green is always entertaining.

    Now, if you really want to get ’em going, take a lot of red dye beforehand and scream the whole time you’re in the restroom. When you’re done, splash some warm water on your forehead so it looks like you’ve been sweating, slam open the door, thrust the sample jar at the attendant and shout “HERE! ARE YOU HAPPY NOW???”

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