Abstract
Hair follicles play a crucial role in skin tumorigenesis, skin homeostasis, and wound healing. They contribute in several ways whereas in the bulge region epidermal stem cells give rise to both normal and malignant skin cells. If mutated, they can potentially lead to skin cancer as is seen in basal cell carcinoma and squamous cell carcinoma, common forms of skin cancer. Various growth factors, such as Wnt, Hedgehog, and Notch signalling pathways, regulate hair follicle development and cycling and dysregulation of these pathways can lead to abnormal cell proliferation and differentiation, contributing to cancer development in hair follicle cells. The stem cells within hair follicles contribute to the regeneration of both the epidermis (outer skin layer) and the hair follicle itself. The regenerative capacity of hair follicles can speed up wound healing by providing a pool of cells that can be recruited to the injured area to promote tissue repair. Hair follicles also modulate the inflammatory response during wound healing by secreting cytokines and growth factors, that orchestrate the healing process by regulating inflammation, angiogenesis, and collagen deposition, but in chronic wounds their role can be disrupted. When the hair follicles are damaged or not activated properly during the healing process, abnormal scarring or fibrosis can occur, leading to the formation of thick, fibrous scars rather than functional skin. The aim of this review is to provide an overview of the many roles played by the hair follicle and its associated structures as well as its close association with the skin.