Why Mosquito Bites Itch
A mosquito doesn't actually bite you, of course. It sucks your blood.
To help enable effective blood-sucking, it first injects anti-coagulant saliva to stop the blood from clotting or forming a scab while it feeds. When the mosquito goes away, its saliva stays in the pocket under your skin.
Now comes the itchy part. Your body releases histamine to fight off a foreign substance. It's the same as an allergic reaction. The histamine causes swelling around the area and as a side-effect it itches.
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