Loss of a single Bak allele fully prevented the hair loss and HF degeneration observed in K5‐Cre/Mcl‐1f/f mice (Fig. 7F), restoring both CD34+ bulge HFSCs and non‐defined HF cell populations, as confirmed by FACS (Fig. 7G, H). This evidence concerns the gene KRT5 and hydrops fetalis.