Wound healing is the process by which skin or other body tissue repairs itself after trauma. In undamaged skin, the epidermis (surface layer) and dermis (deeper layer) form a protective barrier against the external environment. When the barrier is broken, an orchestrated cascade of biochemical events is set into motion to repair the damage. This process is divided into predictable phases: blood clotting (hemostasis), inflammation, tissue growth (proliferation) and tissue remodeling (maturation). Blood clotting may be considered to be part of the inflammation stage instead of a separate stage.