HFSC and components of the HFSC niche. HFSCs (light green) are quiescent during the telogen phase and are found in the outer layer of the bulge and hair germ. K6+ inner bulge cells maintain the quiescence of HFSC in telogen. HFSC activity related to HF regeneration is coordinated with a number of HFSC niches. Around HFs, the skin contains several HFSC niches, including dermal papilla, dermal fibroblasts, immune cells (T cells, dendritic cells, and macrophages), dermal adipocytes, the arrector pili muscle, blood vessels and lymphatic vessels, which regulate HFSC activity.
