There are several reasons for this. The first is usually called a histamine hormone, which is distinguished by a certain type of cell in case of danger of invasion of allergens, toxins and other foreign factors. Such cases include the wound.
Histamine activates the cells of the immune system, while creating the optimal conditions for their operation, that is, preventing the overlap to spread throughout the body (the occurrence of swelling and slow blood flow). The irony of our biological fate is that histamine himself is an allergen that causes, in particular, asthma (swelling of the respiratory tract). Itching in the wound can also be caused by an allergic reaction. The second important factor in the occurrence of itching is the restoration of nerve endings to replace the damaged. In the process of tissue growth, replacing lost, new nerve endings are subjected to constant irritation, which is read by the brain as itching.