Phases of Wound Healing

The healing process is the same for all wounds, whether the cause is mechanical, chemical, or thermal. Health care professionals discuss the process of wound healing in four specific phases: hemostasis, inflammation, proliferation, and maturation (remodeling).

Wound healing process

Hemostasis
The injury causes an outflow of fluid, both blood and lymphatics, at the site. The body activates intrinsic and extrinsic factors to heal. When tissue is damaged, serotonin, histamine, prostaglandins, and blood from the injured vessels fill the area. Blood platelets form a clot, and fibrin in the clot binds the wound edges together. The inflammation stage is initiated during hemostasis, and this process may last a few days.
Inflammation
Lymphocytes initiate the inflammatory response, increasing capillary permeability. Wound edges swell. White blood cells from surrounding vessels move in and ingest bacteria and cellular debris, demolishing the clot and healing the wound. Redness, warmth, swelling, pain, and loss of function may occur. Platelets heavily secrete growth factors during this phase.
Proliferation
Adjacent healthy tissue supplies blood, nutrients, fibroblasts, proteins, and other building materials needed to form soft, pink, and highly vascular granulation tissue, which begins to fill and cover the area.
Maturation
Fibroblasts in the granulation tissue secrete collagen, a gluelike substance. Collagen fibers crisscross the area, forming scar tissue. A new layer of surface cells replaces the layer that was destroyed. New, healthy tissue or granulation tissue appears.
Meanwhile, epithelial cells at the wound edge multiply and migrate toward the wound center. This epithelial tissue will be a light pink “halo” that grows around the edge of the wound until it fills the whole wound with a scar. As it heals, the color will be deposited into the wound that is the same color as the skin.
Over months or years, damaged tissue (including lymphatics, blood vessels, and stromal matrices) regenerates. Collagen fibers shorten, and the scar may diminish in size. Normal function may return, but the scar will only have approximately 80% of the strength of unwounded skin. Alternatively, the scar may hypertrophy, leading to the formation of a keloid and the development of contractures.

Wound healing: partial- versus full-thickness wounds

Partial-thickness wounds are wounds that involve the top layers of skin specifically the epidermal and dermal layers. Partial-thickness wounds heal by epithelization only.

Full-thickness wounds are wounds that extend through the dermis and into subdermal structures.

The more damage that is done to the tissues, the more the mechanisms of healing that are required. Full-thickness wounds will have scar evidence of healing.

Wound healing: acute versus chronic wounds

Simply put, acute wounds progress along the healing phases in an orderly predictable fashion. The mechanism of injury is easily identifiable in acute wounds, for example surgery or trauma. Delays in wound healing are typically minimal and easily addressed.

Chronic wounds are wounds that do not follow the healing process in an orderly, timely manner. Sometimes they “fall off” the healing cascade. Due to various factors, these wounds stall in one of the phases and require long-term follow-up.

Debridement may be used to convert a wound from a chronic to acute one. The debridement activates the healing cascade, and normal healing may commence. All systemic factors must be addressed, or the wound will not continue to heal along the cascade.

Full-thickness wound around a colostomy.

Recognizing wound failure to heal

Sign	Causes	Interventions
Wound bed
Too dry	Exposure of tissue and cells normally in a moist environment to air Inadequate hydration	Add moisture regularly. Use a dressing that maintains moisture, such as a hydrocolloid or hydrogel dressing. Reassess patient hydration status.
No change in size or depth for 2 weeks	Pressure or trauma to the area Poor nutrition, poor circulation, or inadequate hydration Poor control of disease processes such as diabetes Inadequate pain control Infection	Reassess the patient for local or systemic problems that impair wound healing, and intervene as necessary.
Increase in size or depth	Debridement Ischemia due to excess pressure or poor circulation Infection	Reassess the patient for local or systemic problems that impair wound healing, and intervene as necessary. If caused by debridement, no intervention is necessary. Poor circulation may not be resolvable, but consider adding warmth to the area and discussing with the qualified health care professional (QHP). Administer a vasodilator or antiplatelet medication. If caused by infection, apply topical antimicrobials or administer antibiotics, as ordered.
Necrosis	Ischemia	Consult the QHP regarding debridement if the remaining living tissue has adequate circulation.
Too wet and/or increase in drainage or change in drainage from clear to purulent	Autolytic or enzymatic debridement Increased bioburden from increasing colonization Infection	If caused by autolytic or enzymatic debridement, no intervention is necessary; an increase or change of color in drainage is expected because of the breakdown of dead tissue. Choose a dressing that adequately absorbs drainage. If debridement isn't the cause, assess the wound for increased bioburden or for infection. If caused by increased bioburden or infection, apply topical antimicrobials and/or administer antibiotics, as ordered.
Tunneling	Pressure over bony prominences Presence of foreign body Deep infection	Protect the area from pressure. Irrigate and inspect the tunnel as carefully as possible for a hidden suture or leftover bit of dressing material. If the tunnel doesn't shorten in length each week, thoroughly clean and obtain a tissue biopsy for infection and, with a chronic wound, for possible malignancy. Address potential causes of shear if the wound is a pressure injury.
Red, hot skin; tenderness; and induration	Inflammation due to excess pressure or infection	Protect the area from pressure. If pressure relief doesn't resolve the inflammation within 24 hours, topical antimicrobial therapy may be indicated.
Maceration (white skin)	Excess moisture	Protect the skin with skin protective ointment, skin prep spray, or a barrier wipe. If practical, consider a more absorptive dressing.
Rolled skin edges (epibole)	Too-dry wound bed Infection Trauma Overpacking	Correct causal factor. Consider moisture-retentive dressings, antimicrobial dressing. If rolling isn't resolved in 1 week, debridement of the edges may be necessary.
Undermining or ecchymosis of surrounding skin (loose or bruised skin edges)	Excess shearing force to the area	Protect the area from shear, especially during patient transfers. Address potential causes of shear. Consider using a five-layer foam dressing.

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