I think I'm gonna puke.

May 18, 2009 7:54 AM

Why do graphic/gross sights cause nausea?

I'm wondering what the body is doing when nausea results from encountering something gross.

My first thought (a disgusting one) is that it's the body's primal way of warning us not to eat something that's unfit for consumption. We happen across a putrefying carcass, for example, and the nausea it induces prevents us from chowing down. We have to clean up a roommate's drunken bathroom mess, and the nausea tells us "this is really, really not food."

But what about things like a cop seeing a murder scene and vomiting because of its visual or emotional impact? Is the body "accomplishing" something by causing this nausea, or is the nausea an unrelated effect?

posted by Bud Dickman to health & fitness (14 comments total)

It's a good question. I don't have a set scientific answer, but clearly our bigger cerebral cortices allow us the privilege of having conscious/subconscious input into homeostatic mechanisms. You can worry your heart rate and blood pressure up. You can meditate your HR and BP down. High stress can impact your immune system (see the burgeoning field of neuroimmunology, or the journal Psychosomatic Medicine). There's no reason to not expect that you could have similar cognitive/emotional input into emesis.
posted by scblackman at 7:59 AM on May 18 [1 favorite has favorites]

I don't think I've ever had physical nausea from anything I've seen. Really bad odors seem to me to be a much stronger cue to not touch/eat/stay near.
posted by HFSH at 8:05 AM on May 18

I would bet the combination of emotions, hormones from your fight or flight response and the vasoactive reactions your body very rapidly goes through when seeing a gruesome sight, may trigger the nausea and vomiting. The pain center in the brain is very close to the vomiting center, so that explains why some people in great pain vomit. I will have to look into this!
posted by kgreerRN at 8:06 AM on May 18

I'm really going to go out on a limb here, but outside of also suspecting your consumption theory, I imagine some of it is a bit of a modern and Western "ailment," as well. I say this, because I think you will find the understanding of what is gross or horrifying varies greatly from culture to culture, particularly along socio-economic lines or in societies where there is a lot of crime. E.g., if you see people dying of starvation or because of war on a daily basis, you will have different tolerance from the (we'll say) Western cop who'd never seen a dead body until his first murder case.

I could be completely off base here, but it's just an idea.
posted by metalheart at 8:14 AM on May 18

Hmm. Combination of things, I think.

The first real gruesome scene I had to see and deal with in person was a guy whose lower leg was barely attached to the rest of him (as well as some other things, but that was the big one). I felt sick to my stomach because I knew something was viscerally NOT RIGHT about it all.

I think there was also a healthy sense of - fuck, do I not want to look like that anytime soon.

However, the first and only time I ever vomited in relation to something like that was when it was very visually disturbing and I was also intensely afraid. So the combination of "human beings are not supposed to look like that" and fear is what caused that reaction, I suppose.
posted by lullaby at 8:20 AM on May 18

@metalheart -- When I was pondering this, I also wondered whether it's an instinct or a learned behavior, as you suggest. It certainly seems you can be trained to deal with gruesome situations, such as the medical student whose initial reaction to a cadaver is much different from his poise in the ER later on.
posted by Bud Dickman at 8:25 AM on May 18

It doesn't happen to everyone.

One thing to think about, you have what are called the Sympathetic and Parasympathetic nervous systems. The sympathetic activates during a "flight or fight" situation, and the parasympathetic calms you down. When the parasympathetic gets activated, lots of stuff happens.

Actually I don't remember if it's involved with nausea, but the point is there are a lot of systems and they sometimes overlap with eachother's effects. So even though there's not really any good reason to get nauseous or throw up when you see something gross, nerves and PNS activation might be enough to get you to throw up.

According to this: In conditions of very loud noise or unusual anxiety states, the parasympathetic system causes unaccounted-for spontaneous urination, excessive salivary and gastric juices, and either nausea or vomiting.
posted by delmoi at 8:29 AM on May 18 [1 favorite has favorites]

This is pretty speculative, but I think that it's a combination of your stomach associating things that are connected with death and decay with poisoning--one of the primary reasons for vomiting, to rid your body of possible toxins and/or infective agents--and dumping the contents of your stomach in preparation for fight-or-flight, since digestion takes up a lot of the blood supply that would otherwise be used up by the process of getting the hell out of Dodge (one of the reasons why you feel sleepy after a big meal).
posted by Halloween Jack at 8:29 AM on May 18

Another way to put it is that I think it's actually a side effect of the fact that the fight or flight type response is controlled, in part by the same system that controls vomiting when you are sick.
posted by delmoi at 8:30 AM on May 18

This fantastic episode of Radio Lab has an awesome segment in it that talks about the body and brain's simultaneous, visceral reaction to shocking stimuli. The whole episode is a mind-blower, in fact.
posted by Happy Dave at 9:20 AM on May 18 [5 favorites has favorites]

I think that trying to piece together a single cause-effect rationale from a system with multiple feedback loops going on simultaneously is likely to be difficult.
posted by KirkJobSluder at 9:58 AM on May 18 [1 favorite has favorites]

One piece of human evolution has been a tighter intermingling of visceral and emotional systems. Some recent evidence suggests that the same areas of the brain that are driving the response to seeing rancid food are the same ones engaged when we have a social disgust reaction. The response to the food seems to be an ingrained response to keep us from eating food that might harm us. Humans seem to have piggybacked social and emotional aspects onto that response to keep us from situations and relationships that are aversive.

As a whole the disgust reaction seems to be universal across cultures. Darwin was one of the first to investigate it. It it typically identified by an upturned nose, pulling back of the head, and sometimes followed by covering the mouth.

I spend my days researching if the representation of risk and disgust changes across development. Adolescents don't seem to do quite as good a job at it relative to adults. We think it might have a real impact on decision making. What would your choices look like if you had no disgust?
posted by prefrontal at 12:18 PM on May 18

Existential horror.
posted by kirkaracha at 1:48 PM on May 18

Most of the neural network that's responsible for the physical vomit reflex are in the medulla (in the brain stem). There are a lot of projections between this area and a portion of the cortex known as the insula. The insula is implicated in disgust, pain, and the observation of disgust and pain in others. I would speculate that the way the brain processes disgust for things that are likely to be harmful if ingested/touched is piggy-backed by more recently evolved networks that process disgust and related emotions for something like a murder (though a dead body could in some sense also probably produce more visceral "don't eat that" disgust).
posted by solipsophistocracy at 2:11 PM on May 18