Table 1.

Main functions of the growth factors present in platelet-rich plasma

Growth factors	Main functions
PDGF [27]	- Increases hair growth
	- Vascularization
	- Angiogenesis stimulator
TGF-β [29]	- Inhibits hair growth in vitro
	- Hair-cell proliferation and regeneration
VEGF [28]	- Expressed in DP cells in the anagen phase
	- Probably regulates perifollicular angiogenesis
	- Increases perifollicular vessel size during the anagen growth phase
EGF [29, 43]	- Angiogenesis stimulator
	- Hair-cell proliferation and regeneration
HGF [36]	- Angiogenesis stimulator
FGF [29, 43, 44, 45]	- Increases hair growth by inducing the anagen phase of HF
	- Promotes DP cell proliferation
	- Increases the HF size in mice
	- Angiogenesis stimulators
IGF-1 [6, 27, 46]	- Increases hair growth
	- Maintains HF growth in vitro
	- Angiogenesis stimulator

PDGF, platelet-derived growth factor; TGF, transforming growth factor; VEGF, vascular endothelial growth factor; DP, dermal papilla; EGF, epidermal growth factor; HGF, hepatocyte growth factor; FGF, fibroblast growth factor; IGF-1, insulin-like growth factor 1; HF, human follicle(s).