My second poop AskMe
May 5, 2013 4:51 PM   Subscribe

When one strains during defecation and thereby has a little bit of bleeding, why doesn't this cause an infection?

I googled this a bit and it seems it can be a complication from bleeding hemorrhoids, but what I want to know is why, exactly, poop coming into contact with broken skin does not typically result in an infection. If one had a similar skin injury elsewhere on the body, I'd expect exposure to that much bacteria without properly cleaning it would cause problems. Please enlighten me! Thanks.
posted by fozzie_bear to Health & Fitness (8 answers total) 6 users marked this as a favorite
Best answer: IANAD, but those are called anal fissures and, when they get infected, anal abscesses. Straight Dope has some random speculation about why infection isn't super common there (see the last answer in particular), but it does happen.
posted by Monsieur Caution at 5:04 PM on May 5, 2013

IANAD, but my pure conjecture is that the waste left over post-digestion is not necessarily 'dangerous' as it relates to containing possibly infectious material. There's a difference between 'stuff the body cant or didnt absorb' and 'stuff that could cause infections'.
posted by softlord at 5:41 PM on May 5, 2013 [1 favorite]

I have always wondered this as well. My guess is like softlord's: that if you're otherwise healthy, the beasties in your own gut are either stuff that's not terribly pathogenic or is stuff you have a healthy immune response for already (because, y'know, you've been exposed to it already). I've read that it's not terribly dangerous to eat your own poop, even, for roughly the same reason. (I doubt it's a good idea though…)
posted by hattifattener at 5:56 PM on May 5, 2013

If you're healthy and immunocompetent, the bacteria which cause skin infections are not, generally, gut bacteria. For instance, Staphylococcus aureus--the SA in MRSA, though not all S. aureus is MR (methicillin-resistant)--is tolerant of conditions salty enough to inhibit the growth of E. coli.
posted by pullayup at 6:16 PM on May 5, 2013 [1 favorite]

IANAD, but those are called anal fissures

Hemorrhoids are not the same as anal fissures, which are quite a bit more problematic. Even hemorrhoids that bleed a little bit when you poop.
posted by leahwrenn at 6:24 PM on May 5, 2013

IANAD nor am I a microbiologist/ID specialist. That said, I think pullayup has the right idea--gut flora requires some special conditions (i.e., your gut environment) to survive and the skin typically does not provide a hospitable environment for them to grow.
posted by scalespace at 7:59 PM on May 5, 2013

Hemorrhoids are not the same as anal fissures, which are quite a bit more problematic.

I'm still not a doctor, but I'm pretty sure these are very similar, even related conditions (as WebMD says, "Sometimes an anal fissure and a hemorrhoid develop at the same time"). And my understanding is that, in terms of the question, straining that first and directly causes bleeding from torn skin is an anal fissure. Straining that causes hemorrhoids that then tear and bleed is not really better or worse.

Both are common, and neither is usually a big deal, says WebMD. And so far in this thread, I think the most obvious and least speculative reasons why haven't been mentioned, although they come up in the Straight Dope thread.

Anal fissures are tears--bleeds caused directly by straining when you poop or by passing large/dry/hard stool or just by pooping repeatedly too quickly. Usually, they are very small, but they bleed quite a bit, because the area is richly endowed with blood vessels. They also tend to close up promptly, I would suppose because (1) they are flushed clean by the bleeding, (2) they are presumably ragged, little tears that are structurally easy to mend, more like, say, a large pimple that has had some forceful attention than like a paper cut that has those straight sides your platelets have to bridge, and (3) I suspect in most cases they enjoy automatic, strong, and even watertight compression of the wound.

Hemorrhoids are enlarged veins that can be caused directly by straining when you poop, and then, they can also bleed when torn. A doctor can tell you which one you have with a mercifully quick physical exam, and a Google image search, in addition to being super yucky, will illustrate what they're looking for / feeling around for.

Although neither condition tends to be serious, both can become infected. I mentioned anal abscesses previously. But here's a study of the bacteria found in infected hemorrhoids, and although I'm not qualified to conclude much about it and have no idea if the patients involved were immuno-compromised, it mentions numerous bacteria also mentioned on the Wikipedia gut flora page, so the premise of the question that infections don't occur there or don't involve gut flora may not be correct.
posted by Monsieur Caution at 9:40 PM on May 5, 2013

Best answer: Well, all of the above, but your stool is not raw shit, as it were. Each turd is coated in a very thin layer of mucus that allows it to slide along your intestinal tract. The fissures aren't coming into contact with shit, they're mostly coming into contact with mucus. In fact, if you have fissures and open areas of tissue, you're likely to produce more mucus. Because your body doesn't want a staph infection any more than your mind does. Raw sewerage and smeared shit in our environment is a bigger hazard because it hasn't been gift wrapped for the outside world, as it were.

Mucus is awesome.

Hemorrhoids are not the same as anal fissures, which are quite a bit more problematic.

Yup. I am a pregnant lady with a wee little hemorrhoid. It's adorable. They're basically just overworked blood vessels that get swollen, and may protrude from the body. They're still where they always were (more or less), and have the same degree of protection from intestinal flora that they've always had. They're just a smidge more fragile.

A fissure is a tear. You can develop them by forcing from a tightened sphincter a turd that is large and hard and not small enough to pass clearly. You can also get anal fissures from putting things into your anus that are not well lubricated, or that are jagged or roughly edged. Unlubricated anal sex is a great way to wind up with anal fissures.

Two different things. You may wind up with a burst blood vessel if you currently have a hemorrhoid, but that's going to feel different and heal differently than damage done by, say, a poorly lubed plastic dinosaur jabbed up your butt in a fit of paleontological passion.

I do think you're also underestimating how kickass your immune system is. Commensual bacteria that live in your GI tract are going to be "known" to the immune system locally and will be dealt with pretty easily. It becomes an issue only when you have a) a whole honking heap more there than usual (i.e, someone stabbed you in the guts with a sword, mixing your poop into your pelvic cavity) or it gets into somewhere where it isn't meant to be (falling into an open sewer and aspirating raw shit, endangering your lungs). Most of the time our immune system is way hardier than we give it credit for.
posted by Jilder at 11:24 PM on May 5, 2013 [4 favorites]

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