Recent progress in hair follicle stem cell markers and their regulatory roles

Figure 1 Hair follicle stem cells and the hair cycle. Telogen: The length of the hair follicle (HF) is the shortest. HF stem cells (HFSCs) remain quiescent until dermal papilla (DP) releases a new round of stimulations, which activate the hair germ cells at first, then HFSCs. Anagen: The activated HFSCs proliferate and differentiate, forming the outer root sheath and matrix via down growth. After that, the inner root sheath and hair shaft are formed from the matrix. Catagen: The cells in the matrix undergo apoptosis and form an epithelial strand, which retracts the DP. The HF shrinks gradually until entering the next telogen. HS: Hair shaft; SG: Sebaceous gland; HG: Hair germ; DP: Dermal papilla; IRS: Inner root sheath; ORS: Outer root sheath.