Eli5: Why does the body not get used to chronic pain?

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I get why feeling pain is important for us, but why does the body not get used to chronik pain? I dont need to get reminded that my knee hurts for 10 years.

Wouldnt it be smarter if the brain is like: “This nerve is sending me constant signals about pain for years, i should just cut it off”.

In: Biology
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The simple answer to why does it behave the way that it does is because the way it behaves conferred an evolutionary advantage.

I’ll speculate for you and say that organisms which don’t feel pain in injured limbs are more likely to exacerbate their injury to the point where the limb becomes completely useless.

A thought– you never know about the chronic pain your body gets used to, by definition.

A few years back, during and after an acid trip, I found my body “remembered” some old injuries and pain that hadn’t been hurting for a long time. Similarly, I had a problem tooth pulled that I’d forgotten about, but after the surgery my whole neck and jaw felt much more *right*. I realized there had been chronic pain there even though I hadn’t been consciously acknowledging it.

I think we *do* get used to a lot of the chronic shitty things happening in our bodies.

Edit– sorry for using personal anecdotes, but pain is weird and personal and I’m not familiar with the actual science. Will delete if inappropriate.

It can’t do that. Cutting pain off would also remove your ability to feel things in those places. And that’s very bad, because feeling pain is your body telling your brain something’s wrong. You’d be injuring yourself all the time and not noticing.

And then there are folks like me, who are in constant pain literally everywhere all the time. I wouldn’t even be able to move.

Ultimately, the benefits of being able to feel pain outweigh the negative aspects. Being in pain may be miserable, but not having pain can easily cause you to be harmed or even killed.

It does to a degree. I’ve suffered from abdominal pain since I was an infant. I’ve had relatively few headaches. I tolerate abdominal pain much better than I do headaches.

Maybe because the chronic pain is intermittent?

I’ve had an ankle injury that flairs up every few weeks, and is always a little tender and gets sore on any kind of walk or especially if I jump or lose footing. But if I’m just sitting on the couch or laying in bed, it doesn’t really hurt usually.

Pain is an alarm signal, something is wrong when there is pain. In chronic pain, the alarm signal is behaving correctly, there’s often an injury or an inflammation or some structural cause which the alarm is going off to tell you about. Just, we can’t fix the underlying cause sometimes.

My guess would be it doesn’t shut off because the actual system of pain to inform us of bad things happening isn’t the thing misbehaving.

Pain itself isn’t a specific signal, it’s an over or under sent along the nerve, or a disrupted signal, it’s more a check of hey, this isn’t doing the right thing. The check is a good thing, and beyond a nerve block is fulfilling the purpose of telling the body something is wrong, turning it off would be dangerous because injury can still occur to the impacted site, alarm system still needs to do it’s job.

But you can normalise chronic pain – I have chronic spinal headaches, spasticity pain, general nerve pain. It never goes away, even with my meds, but I can tolerate it for much much longer than when it first happened. The pain hasn’t decreased, but my perception of it has changed due to signals like ‘urgency’ and ‘fear’ associated with normal pain being decreased. So some things do get turned off.

This obviously varies but you definitely do to some extent. One reason I hate talking strong painkillers is because when they wear off I’m suddenly aware all these things I got used to ignoring over the years.

Chronic pain is often associated with an increased pain response called hyperalgesia. This is thought to be due to your brain and nervous system going into a state of persistent high-reactivity after experiencing pain. Once this happens, your body can actually perceive pain even when the initial insult is gone.

There is the general mechanism of [neural adaptation](https://en.wikipedia.org/wiki/Neural_adaptation) whereby nerves stop responding to continual input. This is evolutionarily adaptive for most sensation under the maxim “old news is worthless” or perhaps “change is what I need to notice”.

The nocioceptive (pain) neurons are different than the norm, where they discard the typical adaptation because pain is not subject to the same rules. If something continues to feel pain, that “old news” is actually current news and ought not be eliminated. This is an affirmative difference which itself demands evolutionary explanation. Things continue to hurt because pain is useful.