Pathogenesis of scars: An overview

Scars are areas of fibrous tissue that replace the normal skin tissue following injury or disease. The processes of wound healing are dynamic and quite complex. Various factors, including growth factors, turnover of extracellular matrix and genetic susceptibility, contribute to the formation of various types of scars that can be normotrophic, atrophic, hypertrophic, keloid, or mixed. Clinically, keloids and hypertrophic scars are more common in the body areas subjected to increased skin tension, such as the anterior chest, shoulder and upper arm. Recent clinical and basic studies have provided evidence that local mechanical stimulation influences significantly the formation and degree of abnormal scar. The pathogenic role of mechanical force is supported by the preferential growth of the keloid scar along the direction of the skin tension with the characteristic butterfly or crab's claw shape of keloids on the anterior chest being the best example. There has been substantial growth in the basic research regarding the changes in both biomechanical and biophysical properties of cells and their effects on the progression of some human diseases. The interaction between cell and extracellular matrix can not only determine the shape and orientation of cells but also regulate important cellular functions, including migration, differentiation, and proliferation. Identification of the specific signal transduction pathways involved in abnormal wound healing will propel the development of novel methods for scar prevention and treatment. In this Chapter, we will review the orchestrated phases of wound healing process, and the pathogenesis of abnormal scars.