The action of a cosmetic hair treatment on follicle function

OBJECTIVE: Human hair changes with age: fibre diameter and density decrease, hair growth slows and shedding increases. This series of controlled studies examined the effect on hair growth parameters of a new leave-on hair treatment (LOT) formulated with Dynagen (containing hydrolysed yeast protein) and zinc salts. METHODS: Hair growth data were collected from healthy women aged 18 to 65 years. The LOT effect on hair growth was measured in a randomized double blind study and in hair samples; its effect on follicle cell proliferation was assessed by quantifying Ki67 expression in scalp biopsies. The LOT effect on plucking force was determined in an ex vivo model. The effect of Dynagen on the expression of the tight junction marker claudin 1 was analysed in cultured follicles. The effect on protease activity of zinc salts used in the LOT was examined in vitro. RESULTS: Hair growth rate decreased with increasing subject age. The LOT significantly increased hair growth rate, fibre diameter, bundle cross-sectional area, Ki67 expression and the plucking force required to remove hair. Dynagen significantly increased claudin 1 expression in cultured follicles. Protease activity was reduced by zinc salts. CONCLUSION: The Dynagen-based LOT increases hair-fibre diameter, strengthens the follicular root structure and increases hair growth rate.