TCF4 and Hand-foot syndrome: The repair of skin injury is a complex process, in part owing to the mobilization of distinct populations of undifferentiated progenitor cells from adjacent HFs to the regenerating epidermis [8,20] and reportedly contributes, at least in part, through positive regulation of SRY-Box transcription factor 9 (Sox9) and transcription factor 4 (Tcf4), which play important roles in regulating HF morphogenesis and the maintenance of HF stem cells after birth [21,22].