Histamine increases capillary permeability, allowing more oxygen and nutrient to reach the site of injury. This, of course, contributes to healing. Increased capillary permeability also causes plasma to leak into the tissues. This causes pain and swelling which temporarily immobilizes the affected area of the body, allowing for faster healing. Increased capillary permeability also allows clotting factors to enter the injured area.
Blood clots prevent loss of blood.
Histamine also causes dilation of blood vessels, increasing blood flow into the area. This is why injured areas become red and feverish. The increased temperature around the injured area increases metabolic rate which is necessary for the healing process. Once tissue is injured, white blood cells migrate to the vicinity. White blood cells phagocytize bacteria and dead tissue cells, forming a yellowish secretion called pus.