Phases of Wound Healing

Healing is conventionally divided into four phases that overlap rather than succeed one another. Haemostasis occupies minutes: vasoconstriction, platelet plug, and a fibrin clot that doubles as the first provisional matrix. Inflammation runs from hours to about the end of the first week, with neutrophils then macrophages clearing debris and releasing growth factors. Proliferation spans roughly days three to twenty-one and does the construction work, laying granulation tissue, sprouting capillaries, migrating keratinocytes across the defect, and contracting the wound through myofibroblasts. Remodelling then continues for months to years, replacing type III collagen with type I, aligning fibres to load and cross-linking them.

The timescales are the useful part. A sutured wound has only a few percent of its final tensile strength at one week and roughly a fifth at three weeks, which is why closure is not the same as strength, and it plateaus at something closer to seventy or eighty percent of intact tissue rather than returning to full.

An intervention therefore has to be located in a phase before it can be evaluated. Anti-inflammatory action during week one and anti-fibrotic action during month six are different propositions applied to the same wound, and a treatment that helps in one window can be useless or harmful in the other.

The error specific to this literature is the rodent incision model. Loose-skinned rodents close wounds largely by contraction of the panniculus carnosus, while humans close primarily by epithelialisation and granulation, so a faster closure time in a mouse may measure a mechanism people do not have. Splinted models exist to control for this, and studies that omit the splint are weaker evidence than their closure curves suggest.