Why do wounds itch when they are healing

Our skin is a protective cover that shields our vital organs from the adverse effects of the external environment. The moment this protective barrier is broken, the wound repair process begins to bring back the skin to its normal state. The entire healing process can be broadly divided into four phases, which are sequential as well as overlapping.

The first phase is hemostasis during which the platelets are released, which in their turn trigger release of glycoproteins on their cell membranes, and stick to one another to form a mass. Meanwhile, the fibrin and fibronectin are also produced at the injury site. They together form a plug that prevents blood loss as well as traps in the proteins and particles. This plug acts as the primary structural support for the wound until the collagen is formed and deposited.

The second stage is the inflammatory phase during which the polymorphonuclear neutrophils arrive at the injury site and clean the wound by breaking down and phagocytising the damaged tissues, proteins and bacteria. Once the neutrophils complete their task, the macrophages enter the injury site and further remove the damaged tissue and wound debris. The primary objective of the inflammatory phase is to remove the debris and fight infection.

The third phase of wound repair is the proliferative phase during which the vascular endothelial cells form new blood vessels. The fibroblasts grow and excrete collagen and fibronectin, which eventually lead to the formation of provisional extracellular matrix. Simultaneously, the epithelial cells proliferate and form the cover for the new tissue. After all these events have taken place, the wound becomes smaller in size due to the activity of myofibroblasts. These cells function in the same manner as the smooth muscles. They establish grip at the edges of the wound and contract.

The last stage of wound healing is maturation and re-modification phase during which the collagen is remodeled and re-oriented. As the roles of the cells are completed, they are destroyed by apoptosis. In addition to different cells, growth factors are also released during the wound repair, which accelerate the entire healing process.

Now that we have understood the wound repair process, we can easily understand why itching occurs when the wounds heals. During the healing process, all kinds of damaged cells are repaired or replaced, including the nerve cells. As the new nerve cells grow and start receiving and sending signals, itching begins to occur. Unlike other areas where the skin is thick and healthy, in the injury site the skin is undergoing repair, and for this reason, it is quite thin. Hence, the new nerve cells are under a lot more pressure. So, itching is more severe.
Another reason for itching during wound healing is dryness. Together with the skin, the oil glands are also damaged, and the absence of natural oils causes the skin to become dry; as the result itching occurs. Some medical practitioners believe that histamine, which is produced during the inflammatory phase, can also be responsible for itching during healing.