Royal Jelly Induces Thin Hair Shaft Formation by Suppressing Proliferation of Hair Follicle Stem Cells in Mice

Royal jelly (RJ), a honeybee product, is used as a cosmetic and food ingredient to improve skin condition. However, the influences of RJ on hair growth remain unclear. In this study, we investigated whether RJ regulates hair follicle development, hair shaft formation, and proliferation of hair follicle stem cells (HFSCs) using a gentle anagen induction model by shaving the back skin and a forced anagen induction model by depilating the back skin in mice. The results showed that topical application of RJ on depilated skin induced thinning of the hair shaft and smaller hair bulb formation during the anagen phase. In addition, RJ suppressed the proliferation of CK15-positive HFSCs in hair follicles at the early and middle anagen stages of shaved back skin. RJ suppressed the proliferation of cultured HFSCs <i>in vitro</i>. These findings suggested that RJ induces the formation of thin hair shafts by suppressing the HFSC proliferation.