Systemic factors that shape cutaneous pathological scarring.

Cutaneous pathological scars are fibrotic lesions that grow continuously, invade the adjacent skin, and are erythematous, itchy, and painful. Their etiology remains unclear but may involve genetic, local mechanical, and systemic factors. Here, we will summarize the main systemic factors that shape cutaneous pathological scarring, especially keloid formation and aggravation. They include circulating cytokines, chemokines, growth factors, particular cell types, sex hormones, the systemic renin-angiotensin system, and vitamin D, all of which directly shape the angiogenesis, inflammation, fibrosis, and remodeling in pathological scars. There are also several environmental factors that more indirectly influence pathological scar formation or progression, namely diet, smoking, psychological stress, and exercise. Notably, much of the evidence on these systemic factors focus on their effects on one pathological scar characteristic, namely their fibrosis. However, systemic factors probably also shape other pathological scar characteristics. We describe two new avenues of keloid research that may greatly improve our understanding of pathological scarring and the systemic factors that affect it. One is the multiple similarities between keloids and tumors; the other is the different stem-cell populations in keloids. We expect this research will greatly aid the development of diagnostic biomarkers for cutaneous pathological scars and drugs/techniques/regimens that prevent, improve, or cure these scars.