Fibroblast Growth Factor 5 （FGF-5） is a member of the fibroblast growth factor （FGF） family, which plays a crucial role in various cellular processes, including cell proliferation, differentiation, and survival. FGF-5 is primarily known for its involvement in regulating hair growth and cycling. It is expressed in the hair follicles and acts as a negative regulator of hair follicle growth. FGF-5 signaling is essential for the transition between different phases of the hair growth cycle, including the growth phase （anagen）, regression phase （catagen）, and resting phase （telogen）. Dysregulation of FGF-5 expression or activity has been linked to hair loss disorders, such as alopecia, highlighting its importance in hair follicle biology.