Why are wounds itchy? It seems counter productive for you to scratch at a scab or wound.

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Or is it a bacterial/viral infection causing the itchiness to propagate?

In: Biology
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The healing process does impact your body; the scab will tug on the skin a bit, and there may be some inflammation. The itching/scratching sensation is your body’s sense of touching telling you something is wrong in that area. These two systems are working independently, so your sense of touch is just reacting to this tension on the skin.

It’s counterproductive, sure, but our bodies aren’t perfect. And if this isn’t posing a significant problem to our evolutionary purpose (to survive long enough to reproduce), then there won’t be any evolutionary pressure for this to change.

Injured cells and the cells that do the work of healing release molecules called cytokines to communicate with each other so that the right cells are doing the right things at the right time. These are the same kinds of things of molecules you hear about in “cytokine storm” that can be such an problem in Covid infections. Sometimes the effects of these chemicals are useful, sometimes they are annoying. Histamine, for example, might help you to get rid of something irritating by sneezing or scratching, but the itchiness might also be annoying in a healing wound. Also, when blood in an old wound or bruise breaks down, it becomes bilirubin, which just happens to be something really itchy.

I thought it was to attract more blood to the area by irritating it. More blood is more nutrients so it heals faster.

At least that’s what I told myself when I scratched around my myriad sutures a while ago.

Scratching or rubbing the area around a wound could temporarily increase blood flow (and move lymph around).

I don’t think we know the answer to this. Itching is mysterious and lives between pain and pleasure. Many wounds never itch and some itchy things have nothing wrong with them. The fact that scratching seems to feel good or at least alleviate the itch is interesting and suggests this is the “goal” of the itch. It could be an evolutionary remnant, or something that imparts just enough of a survival / reproductive advantage to be preserved. One thing for sure is that pain is absolutely critical to survival as it serves as an early warning sign of infection. Pain Nerves in teeth (which are basically holes in your skull surrounded by massive amounts of bacteria) are notoriously easy to trigger responding to almost all stimuli as painful including heat, cold, pressure, vibration and chemical changes. That’s not itching but I think itching is sort of a compromise between pain and ignoring the sensation. Pain can make you favor the painful area, where as itching attracts your attention. Slivers for example sometimes don’t hurt but they can itch. If you are animal with fur, you can’t see the irritation and you can’t pull it out with your claws or hooves, but you can sure scratch at it.

Another thing to keep in mind is our “animal past”, as a lot of evolution effects stem from that.
When you don’t have hands and something itches… you lick it. Just like animals do. And that has the effect of cleaning the wound and the salvia is mildly antiseptic as well.

Not entirely an answer to the question as someone else already answered it, but picking at a scab does to a cretsin degree help it heal better. Scabs collect dirt and grime, if it cracks or gets something underneath it, the wound can quickly get infected. In some cases its beneficial to have a fresh scab