Mechanics of scars.

When a wound heals, as everyone has observed, it contracts, thickens and wrinkles the neighbouring skin, forming a scar. The morphology of the scar depends on the type of wound; an urgent tracheotomy leads to a very different scar than a carefully planned face lift. The surgical challenges of intrusive procedures such as removal of skin lesions, skin transplantation or grafting, and scar removal are complicated by the complex geometry and stress states in different parts of the body. We show that, for relatively general conditions, the nature of the localisation of the scar is determined by the background tension of the skin which can arrest the formation of wrinkles around a scar. Our physical experiments to simulate this procedure indicate that the region deformed by the defect has a characteristic length scale r* approximately 1 square root of tau, where tau is the natural tension of the skin.