A growth factor is a naturally occurring secreted protein capable of stimulating cell proliferation, wound healing, and cellular differentiation. Growth factors are important for regulating a variety of cellular processes and typically act as signaling molecules between cells.

Different growth factor families including the epidermal growth factor (EGF)-related ligands, fibroblast growth factors (FGF), transforming growth factor-beta (TGF-beta), insulin-like growth factor (IGF), hepatocyte growth factor/scatter factor (HGF/SF), and platelet-derived growth factor (PDGF) have been shown to be crucial for the regulation of the hair cycle and hair growth.