Your body has different ways of signaling there is a problem, or sometimes drawing attention to a problem in a particular area.
Part of the healing process is your body produces a chemical called histamines. These histamines serve various purposes, but in healing process they cause blood vessels to dilate (open up) and helps cells/repairing functions/blood/nutrients begin the healing process.
The histamine causes the itch as an effect as well. The area becomes inflamed in the healing process.
When wounds heal, your sensitive nerves send a signal to the spinal cord that the skin is being stimulated, and in this particular case your brain interprets this stimulation as an “itch”. Once the wound heals, there is no longer a need to produce histamines, the site is no longer agitated/inflamed and the itch stops.
“Most wounds, large and small, go through a four-step healing process.
Step 1: The bleeding stage
Also called the hemostasis stage, this is the point that the injury occurs. Your body responds to the injury by activating an outpouring of blood, lymphatic fluid, and coagulation (clotting) to stop the loss of blood.
Step 2: The defensive/inflammatory stage
This is the beginning of the repair process. It starts immediately after the injury occurs and typically lasts up to six days. Your body sends white blood cells to combat harmful bacteria at the wound site, swelling at the wound site starts and the skin begins the repair process.
Step 3: The proliferative stage
Commonly lasting anywhere from one to four weeks, the proliferative stage is also known as the granulation stage or tissue-regrowth stage. This is where you can see the signs of skin repair: scabs protecting the new skin cells that are growing.
Step 4: The scarring stage
Also referred to as the maturation phase or remodeling stage, this stage can last from three weeks to four years. During this stage, the scab falls off as the new tissue gains strength and flexibility and collagen fibers form scars.”
Via [here](https://www.healthline.com/health/why-do-scabs-itch#healing-process)
Sometimes even if you don’t have physical wound, these histamines can cause a crazy response. Your body overacts and activates your immune system when there isn’t actually a threat (think dog allergies).
Think of anti-histamines medication that people take when they have allergic reactions- like hay fever, or when you scratch a misquote bite.
Edit:
I’m overly sensitive to mosquito bites myself, and have seasonal allergies. So I get super itchy skin at the site of a bite, and the bite puffs up a little more than usual.
For seasonal allergies I take Aller-clear (like Allegra). [See here it’s an Antihistamine](https://www.rxlist.com/allegra-side-effects-drug-center.htm) if I don’t, my eyes get super itchy, and nose, sometimes throat etc.
I did a pain management course once and learnt that itching is actually on the pain continuum. It’s a very mild pain signal.
I suppose the survival value is that it keeps you aware of the wound and perhaps helps you avoid damaging the vulnerable area while it completes healing. (Except if you scratch it!)
As it heals the wound goes from painful to itchy to healed.
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