Itching is a common symptom during the healing process of a wound. The itching sensation can range from mild to severe and can be very annoying and uncomfortable. But why exactly do wounds itch when they are healing? There are several reasons this occurs.
Inflammation
In the initial inflammatory phase after an injury, various cells and chemicals arrive at the scene to promote healing. This includes immune cells like mast cells, basophils, neutrophils, lymphocytes, and macrophages. When these cells are activated, they release substances that cause inflammation like histamine, serotonin, bradykinin, and prostaglandins. These inflammatory mediators trigger nerve endings in the skin and cause itching and pain sensations. The inflammation helps fight infections, remove damaged tissue, and pave the way for tissue regeneration.
Nerve fiber sprouting
As a wound heals, new nerve fibers sprout in the area as part of the regeneration process. This nerve fiber sprouting occurs as early as a few days after an injury. The new nerve fibers are more sensitive and can become easily irritated, sending itching sensations to the brain even with minor stimuli like contact with clothing or scabbing.
Dry skin
A healing wound often produces flaky dead skin cells and scar tissue that can become very dry and itchy. The dryness also results from the wound healing steps that remove oils and moisture from the skin surface. The lack of moisture and natural skin oils leads to irritation of nerve endings and itching.
Scarring
Scars form as a natural part of the healing process after deeper wounds. Scars have a different texture compared to normal skin tissue. As the scar matures and shrinks, it can tug at nerve endings in the surrounding skin and underlying tissues, producing itching.
Re-epithelialization
In the epithelialization phase of wound healing, new skin cells migrate and proliferate over the wound bed to cover it with a protective barrier. This process of re-epithelialization can cause mild itching as the keratinocytes reform connections with nerve cells in the dermis layer underneath.
Histamine
Histamine is released by immune cells like mast cells and basophils as an inflammatory response to injury. Histamine helps widen blood vessels to improve blood flow to the wound site. But it also binds to histamine receptors on nerve cells and causes itching. Antihistamines can provide some relief by blocking the action of histamine.
Growth factors
Growth factors like platelet-derived growth factor (PDGF), epidermal growth factor (EGF), fibroblast growth factor (FGF), and vascular endothelial growth factor (VEGF) increase in a healing wound. They promote cellular proliferation, new tissue and blood vessel growth. But these growth factors also act on nerve fibers to cause itching.
Neuropeptides
Substance P and other neuropeptides are produced in sensory nerves after a skin injury as part of the inflammatory response. Like histamine, they bind to receptors on nerve fibers and cause itching by altering pain signaling pathways.
Tactile stimulation
As a wound heals, the new skin tissue remains sensitive to touch and pressure. Clothing brushing over the wound or scab removal can provide enough tactile stimulation to trigger itching by activating peripheral nerves.
Pruritogens
Bacteria, allergy cells, and other agents can sometimes infiltrate a healing wound and release substances called pruritogens that directly provoke itching by interacting with nerve cell receptors. For example, staphylococcus bacteria can generate pruritogen biofilms.
Nerve compression
For deep tissue wounds, inflammation, swelling, and scar tissue formation can put pressure on nerves adjacent to the injury site, leading to neuropathic itch signals.
Psychological factors
Emotional states like stress and anxiety can worsen wound itching by increasing inflammation and altering neurological pathways for itch perception.
When does the itching peak during healing?
The itching associated with a healing wound is often most intense a few days to about 1-2 weeks after the initial injury. This correlates with the inflammatory, epithelialization, and early proliferation phases of healing when factors like histamine levels, nerve sprouting, and cell growth peak.
Does the itch mean the wound is getting infected?
Not necessarily. Mild to moderate itching is normal during wound healing and does not always indicate an infection. However, severe, persistent itching or itching associated with other symptoms like wound pain, redness, swelling, oozing pus, fever or red streaks spreading from the wound could signify a possible underlying infection that should be evaluated by a doctor.
Why are some wound locations more itchy than others?
Highly sensory regions of the body tend to experience more wound itching. For example, wounds on the face, back, hands, and feet often itch more due to increased nerve fiber density in the skin of these areas.
Does the itch indicate the wound is healing slowly?
No, severe itching does not necessarily mean slow or impaired healing. Itching severity depends on the individual and location, not the biological healing rate. Even normally progressing wounds can itch intensely due to inflammatory factors and nerve sensitivity in that area of skin.
Conclusion
While annoying, itching is a normal part of the intricate healing process for wounds. It results from a cascade of immunological and cellular events that occur in tissue repair after injury. The sensory nerves in the skin make itching the predominant sensation during wound healing compared to pain. While severe or persistent itching can indicate complications, mild to moderate itching is an expected side effect of the inflammatory and regenerative processes of healing.