Intrinsic Modulators of Hair Growth: Roles of Growth Factors, Cytokines, Chemokines, and Interferons

Hair growth is regulated by a complex interplay of intrinsic factors including growth factors, cytokines, chemokines, and interferons (IFNs), which either stimulate or inhibit hair development. This review investigates the specific intrinsic factors involved in hair growth regulation through a comprehensive analysis of studies examining both in vitro and in vivo models. Key growth factors, such as hepatocyte growth factor (HGF), growth hormone, vascular endothelial growth factor (VEGF), fibroblast growth factor, and epidermal growth factor play significant roles in modulating hair growth through diverse mechanisms. For instance, HGF promotes hair growth through DNA synthesis and elongation, whereas VEGF does so by enhancing vascularization. Cytokines also play critical roles; interleukin (IL)-1 and IL-6 have been demonstrated to inhibit hair growth, whereas IL-4, IL-12B, and IL-15 are stimulatory by prolonging the anagen phase and activating dermal papilla cells. Chemokines, such as CXCL1, CCL2, CCL5, and CCL9, promote hair growth by macrophage recruitment and altering signaling pathways (i.e. nuclear factor kappa B pathway), whereas C-X-C motif chemokine ligand 12 inhibits hair growth by delaying telogen-to-anagen transition. Finally, IFN-β and IFN-γ generally inhibit hair growth by prematurely inducing the catagen phase. Understanding these intrinsic factors not only provides insights into healthy hair development but also offers the potential for developing targeted, personalized interventions for hair disorders. However, given that most of the data are extrapolated from human in vitro studies or animal in vivo experiments, further research involving human subjects is necessary to strengthen and validate these findings.