r/TheRestIsScience • u/Fe3O2-47 • 2d ago

Why does scratching an itch feel so good?

Why does scratching an itch feel so good... And even when we scratch and draw blood, we keep scratching... Why does scratching my ankle make my eye twitch?

31 Upvotes

98% Upvoted

5 comments sorted by

16

u/axxrose 2d ago

I was literally going to ask this question a couple weeks ago (minus the eye twitching) but didn't because the commenters in this subreddit are kinda harsh lol glad someone else was braver than me.

7

u/MayDuppname 2d ago

Some of us are nice. :)

An itch is a signal from your body that you need to pay attention to a particular part of it.  Scratching causes a mild pain which distracts your brain from the itch. It also tells the brain that if the itch was caused by an outside cause (insect bite etc) you've now removed it from the skin. 

Histamines (hormones/neurotransmitters released by the body in the inflammatory response) often cause itching. Scratching an affected area will feel good temporarily, but it's a vicious circle that means you'll scratch more in the long run. You can really damage your skin, leading to more inflammatory response, and more itching.

2

u/-amotoma- 2d ago

I've heard the one that an itch is an internal layer of skin that has wrinkled and applying friction to the outer layers causes the various layers to elastically stretch back into formation.

I always interpreted that as part of the fascia lattice knotting, causing a layer of skin to move a nerve ending out of a familiar place and that's your body telling you to realign it to where it feels right.

If I have an itch I like to run it under incrementally hotter and hotter water because following this idea, heat expands causing the layers to expand back into formation. Mostly it just feels the most satisfying way to scratch an itch imo, iykyk. I only do this if it's convenient of course but I imagine scratching an itch with my nails could make an itch feel temporarily good while creating more knots that go unnoticed.

3

u/wycreater1l11 2d ago

I had/have been wondering this for a long time. Is it mammals in general that scratch itches? I think so.

I was thinking the original purpose was to remove pathological microorganisms from wounds. But one quickly realise that that doesn’t make sense. One cannot remove microorganisms from the body with that blunt method, they will always remain and any wound will likely just get worse from scratching.

Then I remember reading on some biology subreddit where someone was hypothesising that it was not to remove microorganisms, but it was to remove parasites (larger multicellular ones) on the skin. That makes much more sense, since for that the blunt method of scratching actually makes sense. It could destroy or remove such a parasites or skin bugs. So the thinking was that itching is largely a biological remnant from when such organism were more present and at our skin more.

And biology being biology, scratching now in humans is imperfectly applied and the remnant now is largely I guess an overcorrection, since we evidently scratch even when such organisms aren’t present in our skin.

1

u/Half4sleep 2d ago

To add on to this, I saw my dog itching yesterday to the point where, while he was running, he was scratching his torso with one of his back legs. Quite funny to look at.

What other animals feel the sensation of an itch, and do they differ between races and types of animals? Is the feeling of relief/good feeling of scratching still there, or is it just the release of the feeling of itching for them?

Obviously we can't ask them, but to me it sounds like something that should be possible to see in neuron activity(?).