The bulge SCs were the first population of HF-SCs discovered in the 1990s [114] and have been shown to be Krt15+ and to give rise to all the lower epithelial cell lineages of the HF, i.e., outer root sheath cells, matrix cells, the companion layer, three layers of inner root sheath cells, the hair cuticle, the cortex and medulla. Here, KRT15 is linked to hydrops fetalis.