Scientists showed that a powerful melanin‑stimulating peptide can pass through human skin samples in a lab setting, staying intact and still active. The amount that gets through depends on where on the skin it’s applied and how thick the skin layer is. This is the first lab proof that a melanotropic peptide could be delivered topically, hinting at future skin‑tanning or pigment‑restoring creams, but it’s far from a ready‑to‑use protocol for DIY users.

A superpotent analogue of alpha-MSH, (Nle4,D-Phe7)-alpha-MSH, when applied topically to mice induces darkening of follicular melanocytes throughout the skin. In vitro studies have demonstrated delivery of the peptide across mouse but not rat skin. This variation in permeability of skin of animal models prompted us to use human skin in vitro. The melanotropin was applied to the surface of human skin samples through a permeation apparatus and allowed to penetrate for 24 h at 36 degrees C. Passage of the analogue was shown by both bioassay and radioimmunoassay. These assays correlated well and demonstrated both the presence and the biologic integrity of the peptide after transdermal passage. Regional differences were noted in the degree of transdermal penetration. In addition, split thickness skin allowed greater penetration suggesting dermal binding of the hormone. This study is the first to show that a melanotropic peptide can be delivered transdermally through human skin in vitro. This has potential importance in the development of therapies for hypopigmentary disorders and for the stimulation of skin tanning without ultraviolet light.