Wound healing happens in four overlapping phases that run from minutes to more than a year. A wound that stalls in one phase becomes a chronic wound.
Stopping the bleeding
Vessels narrow, platelets stick together and a fibrin clot seals the wound within minutes. The clot also acts as a frame for the cells that come next.
Inflammation
For the first few days, white cells clean the wound of microbes and debris. Some redness, warmth and swelling at the edges is normal at this stage.
Rebuilding
From about day 4 to week 3, fibroblasts lay down collagen, new capillaries grow and red, bumpy granulation tissue fills the wound. Edges contract and epithelial cells cover the surface.
Remodeling
Over months, collagen is reorganized and the scar flattens and pales. A healed scar reaches only about 80 percent of the strength of normal skin.
What slows healing
Infection, poor blood flow, diabetes, smoking, poor nutrition, steroids and pressure on the wound. Wounds closed with sutures heal by primary intention; open wounds heal from the base up by secondary intention.
| Phase | Timing | Main event |
|---|---|---|
| Hemostasis | Minutes to hours | Clot forms |
| Inflammation | Days 1 to 4 | Cleaning by white cells |
| Proliferation | Day 4 to about week 3 | Granulation tissue, new skin |
| Remodeling | Week 3 to 1 year or more | Scar strengthens and matures |
At the bedside
At each dressing change, note the size, wound bed, drainage and edges, and watch for spreading redness or pus. Timing of suture removal depends on the site, from about 5 days on the face to 10 to 14 days over joints.
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Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).