When you scratch a mosquito bite, you damage some cells. Damaged cells release histamine, which causes localized swelling. The swelling can crush cells, causing them to release more histamine. This is an example of

Positive feedback.

Explanation:

Positive feedback is a process in which the end product of an action cause more of that action to occur in a feedback loop.

Inflammation is thhe local reaction of bodily tissues to injury caused by physical damage, infection or due to any allergic reaction. Injured tissue mast cells release histamine, which causes surrounding blood vessels to dilate and increase permeability. This allows fluid and cells of immune system to leak from bloodstream through vessel walls and migrate to site of tissue injury or infection where they fight infection and heal injured tissues.

of a cycle where scratching will cause even more of an itchy sensation