Why does feces smell so bad?

So I’m taking a nice growler last night, and it stinks real bad. I got to thinking, why does it smell so bad? Also, why does it have the potency to strip paint off of the bathroom walls some days, but other days barely smell at all? I did a search, and found that feces is usually brown because of bilirubin or decomposed red blood cells secreted by the liver. Is this same substance responsible for the horrendous smell I produce or is it something else?

There are two answers to this- one biological and one metaphysical. I think what you are going after is the biological answer, so let me pose the same question to be addressed by the philosophers on the board:

If feces smelled like roses, and roses smelled like feces, would feces still stink? In other words, does feces stink because of what we perceive it to be? (i.e. human waste) And it therefore follows, do all things that we claim “smell like feces” repulse us because their aroma reminds of of human waste?

Feel free to think about this while sitting on the toilet.

IIRC, the “stink” is methane, produced by the E. Coli bacteria (a good variety) in your colon. They’re just chowin’ down on the parts of your food (e.g., cellulose) that you can’t digest.

So I suppose that when “your shit don’t stink”, you haven’t had much food that your E. Coli can eat, so there’s not as much methane in your movements.

The bilirubin is put into your digestive tract because that’s the easiest way for your body to recycle the proteins, by having them broken back down into amino acids by the most efficient means available. Ultimately, I think it’s the iron in the remains of the hemoglobin in the bilirubin that colors your stool brownish. (I noticed that when I took iron-fortified vitamins, my stool got much darker.)

Basically, it stinks because our ancestors were somewhat healthier than those who thought it smelled good. Over a few thousand generations, that makes a big difference.

There are a few drawbacks, but it won’t be such a drawback if, for whatever reason, it becomes a good enough advantage to like the smell of shit.

Attrayant, that is a great question. I would say that it does stink because of what we perceive it to be. I’d bet that if you cooked some food in a bathroom that people normally think smells good, and removed the food and somebody went in there, that they would comment on the stench. Also, I find that I can stomach my own putrid emissions more so than those that others have left behind for my smelling pleasure. With that in mind, I believe that perception plays a big role in how bad poop “stinks.”

AWB, thanks for the info.

Brain fart, the first ‘drawbacks’ should be ‘throwbacks’. Probably shouldn’t post stoned.

It IS a matter of perception. It doesn’t stink if you’re a maggot or other vermin.

AWB: I think you’ve got two different issues mixed up here.
Bilirubin is the breakdown product from red blood cells and has a structure related to haemoglobin (but ring opened). It is not ‘put’ into the digestive system for any reason other than to be excreted, and it does not contain any protein or amino acid.

I was under the impression that methane was odourless, but I’m not so sure now that I think about it.

The body (re: proteins) does not excrete proteins or amino acids which it hopes to re-adsorb, AFAIK. Wouldn’t it be rather a wasteful strategy?

What smell you get depends on what you eat/drink basically.

if its yellow, let it mellow
if its brown, flush it down

  • old saying

[semi hijack]
android209 - Uric acid & urea salts are produced from the ammonia produced when the body breaks down excess proteins/amine structures (either because more is eaten than is needed or from recycling/catabolic processes in the body). Since ammonia is very toxic to the body, the nitrogen compound is handled in the form & excreted in urine…some is reabsorbed to be reused, but much is lost in sweat & urine. The amount lost would depend onthe amount currently present in the bloodstream at the time of passing through the kidneys…if there is very little in the blodd, it will be reabsorbed, if not, it won’t be. A simple way of only losing it when it is truly spare. Desert animals & some salt water fish can excrete pure uric acid crystals, saving on water loss.

A quick guide to urea excretion with some further reading suggested

AWB Re the bilirubin issue…as WIGGUM noted, we have had threads on this before if you search on it, but in brief it is yellow-red & bacteria in your gut break some of it down into another stage which is colourless - Urobilinogens and the rest of this is converted to stercobilin (same link) which is brown. Also, it is not iron in the bilirubin that gives it the colour as it doesn’t contain any - the main point of breaking down the red blood cells is to recycle the iron from the diet. The iron gets store din the body attached to ferritin, mostly found inthe liver, spleen & bone marrow, with some carried in the blood itself. It is not an excretion compound. If you were slightly anaemic before it might have upped your rate of production of new ones & hence more cells around in a few weeks time to be broken down, so that you had more bilirubins around to get turned brown…

some links on bilirubin & it’s formation:
http://web.indstate.edu/thcme/mwking/heme-porphyrin.html - this one also has some interesting stuff on the cause of the colouration of bruises lower down.
[/semi hijack]

Methane is an odourless gas. The smell is caused by hydrogen sulphide which is also produced by bacteria in your gut…and probably other “aromatic” (trust me, it’s a chemistry word) & inorganic compounds that are odiferous & volatilise easily to produce a smell…

On a related note, does the smell of feces escape from the toilet water. I can understand why the smell would spread if I had a case of the Hershey squirts and created a “stew” in the toilet, but what about solid movements? Once under water can the smell escape or does the smell escape during the second or two between the bunghole and the pot when the waste is airborn? If the latter is true, it must be a highly potent aroma.

Useful information fierra, but I’m not quite sure why it’s aimed at my original reply, given my assertions that bilirubin is a non-protein/amino acid related product from haemoglobin breakdown and that proteins and amino acids are not reabsorbed once excreted into the digestive tract. Does your reply alter my (limited) information?

I’d agree that H[sub]2[/sub]S is a major component of the odour, but other aromatics (meaning benzenoid)? I can’t think of many aromatic compounds which are excreted and are sufficiently volatile to be detectable.

On the topic of reabsorption, are we talking about the same thing here? I’m not talking about readsorption to the blood stream from the kidneys or other temporary storage site, but rather the possibility of readsorption after excretion to the bowels (how unscientific:)) and bladder. I wasn’t aware that that occurred, except perhaps in the case of water.

As for the uric acid trick, I think a few birds have mastered it too. Must be damned uncomfortable;)

android209 - it was aimed at this bit…

I think there are other sulphate compounds in there somewhere…and other hydrocarbons than methane (& I shall now go & write out a hundered times “I must not attempt chemistry puns in gq”). Quite how pungent & volatile these compounds are is another matter - and one I don’t really want to pursue any research into… :wink:

I’m sorry, I was just covering off the protein reabsorbtion/recycling aspect of the bit of your post that I quoted above.

However, since the bilirubins are put into the small intestine, which is where the majority of absorbtion of digestive products takes place, there is time for the bacteria to break it down a stage & for some of the urobilinogen to pass though the gut wall and back into the body…however, they undergo eactly the same sort of treatment again - some is excreted in urine this time, & some returned to the liver to be excreted via the gut again.

One has to keep in mind that something smells “bad” or “good” based only on the type of signal sent to the brain by the cells in your nose (whose receptors are activated by molecules of whatever you’re smelling). We evolved to get the “bad” signal from our feces so we wouldn’t eat it and the many billions of bacteria in it.

FYI, In Japan one can buy a pill that neutralizes the smell.
Seems to be a big hit over there.

If the technology really exists, I’m surprised nobody’s tried adding it to baby formula. Of course, the FDA would raise a stink.

Personally, I enjoy the smell of feces.

The ‘stinkless poop’ pills were originally intended for use in nursing homes, to make things a little easier on caregivers who have to change adult diapers all day. The sudden demand for the product among younger people (usually women) caught the manufacturers by surprise. Since then, a number of doctors have warned against using these pills, as the early indicator for a number of health problems supposedly is a change in fecal smell, which would go unnoticed in someone whose shit don’t stink.

With that last concern in mind, it seems unlikely (though not impossible) that it would be approved for use in baby foods.


More research reveals that it’s hydrogen sulfide that stinks.

Uhhh, it’s not hydrogen sulfide either, unless you’ve been eating a lot of eggs lately. H2S has a very strong “rotten egg” smell, simply because that’s a gas eggs happen to give off when they rot. Your nose is extremely good at detecting H2S, so a little goes a very long way. The smell of the feces is principally due to the compounds indole and skatole.

I once saw a bottle of ammonium sulfide packaged as “Morning Breeze” for use by low life type practical jokers. PHEW did it stink, and was reminicent of what you might pass some hours after eating a meal of cooked cabbage in garlic sauce with soup beans cooked with bacon and onions. This leads me to believe you body might be producing some of this stuff as well. However, your typical fart does not usually smell exactly like feces, however bad it may be…

On a couple of side note, H2S is quite poisonious, more so than cyanide, and in toxic concentrations it deadens the nerves in your nose to the point you can no longer smell it. Methane is odorless - the smell you get from gas stoves and furnaces is ethyl mercaptan - C2H8S - which is one of the very few things that smells worse and can be detected in even lower concentrations than H2S. The gas company adds ethyl mercaptan so you can detect even the tiniest leak in your gas lines.