why does it itches when a wound starts healing:

Itching is due to the release of chemical substance, called histamine, which stimulates nerve endings. Histamine is a decarboxylated form of amino acid histidine, a powerful vasodilator present in animal tissues. When tissues become inflamed as a result of bacterial invasion, or trauma such as a cut, chemicals or heat, histamine is released from mast cells in the tissues. This increases the blood flow and permeability of blood capillaries in the wounded area. Apart from this, the number of basophils also increases during healing. Basophils contain relatively large amount of histamine. Histamine from the basophils and from the surrounding cells diffuse into the skin nearby and stimulates the nerve endings, which leads to itching.