FIGURE 1.

Timeline of normal human cutaneous wound healing. Wound healing following hemostasis takes place in three overlapping stages: inflammation, proliferation, and maturation/remodeling. While differences exist in the soft tissue defect repair process between different species, developmental timepoints, and anatomical sites, the fundamental steps are conserved in the vast majority of examples of adult mammalian wound healing. During the inflammatory phase (which peaks at 24–48 h post-wounding and lasts for several days), immune cells such as neutrophils and macrophages debride the wound, eliminate contaminating microbes, and secrete an array of cytokines and growth factors to recruit other cells involved in healing to the wound site. The process of re-epithelialization begins within hours of injury and accomplishes wound closure over the course of days to weeks by reestablishing a functional epithelial cell barrier. The proliferative phase (which begins 4–5 days after wounding and may last for several weeks) involves the formation of granulation tissue (by fibroblasts, endothelial cells, etc.) as a temporary substrate to fill the soft tissue defect. Finally, during the maturation/remodeling phase (the longest stage, beginning at approximately week 3 post-wounding and lasting for as long as 1–2 years), the wound bed becomes less cellular via apoptosis, and the extracellular matrix is remodeled to gradually increase in strength.