I have eczema, and I feel like most people who don’t have it cannot understand the experience of giving in to the urge to scratch affected skin after a period of trying to resist it. The best way I can describe it is an orgasm, the length and intensity of which you can directly control. It really is that intense. Why would we have evolved to have such an extreme pleasure response to something negative? And yet the effect of scratching on the skin seems very clearly negative. As a sufferer, it’s psychologically very difficult and confusing.

For persistent itches, a most effective remedy I've found is to pour hot water on it. Not burning - but as hot as you can possibly stand without burning. The hotter the better.

It is only briefly painful, but it kills itches completely. I don't know why it works, but it definitely does work.

Hmm but this was an allergen, where having more white blood cells at the site isn't beneficiary. If it was bacteria or a parasite, then the story might be very different.

Ages ago I started trying to scratch itches through some fabric, like a shirt sleeve or something, so I wouldn't damage the skin (keep the fabric stationary on the itchy skin and drag your hand across the fabric). For some reason it's almost as satisfying as scratching directly, so I wonder if it gets the benefit without the downside here.

This article was about itching due to bug bites or skin disease. In my case, my back sometimes develops several itchy spots as I undress for bed. I use a back scratcher, not too heavily, the itches seem satisfied, and don't return. There's no skin damage that I'm aware of. I find it hard to believe that this is somehow harmful.

Lab Mouse is officially the worst job in the world.

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I always thought the dry skin causes the itch (when I don't see any bug bites). So scratching would relieve us from dry skin. But, I learned something today.

We already knew that scratching causes an inflammatory response. Where the specific mechanisms involved that the study found previously unknown?

(editted to reword my question)

I always figured it was just to increase blood flow. That's the reason that hot water also satisfies the itch, it increases blood flow as well.

... but it hurts so good!

(in mice)

tl;dr Scratching an itchy spot boosts the local inflammation and immune response.

I know people hate the "just so" stories, but from an evolutionary perspective it makes sense. You get a parasite, it itches, you scratch it, which removes the parasite and kicks up the local immune response.