Pinus thunbergii bark extract rich in flavonoids promotes hair growth in dorsal skin by regulating inflammatory cytokines and increasing growth factors in mice

Korean maritime pine bark ( ) has been used as an alternative medicine due to its beneficial properties, including anti‑inflammatory effects. To date, the anti‑inflammatory and hair growth‑promoting effects of bark extract have remained elusive. Therefore, in the present study, bark was extracted with pure water (100˚C) and the extract was examined to determine its polyphenol and flavonoid content. C57BL/6 mice were used to assess the effects of the extract to promote hair growth. The extract (1, 2 and 4%) was topically applied onto shaved dorsal skin and hair growth was observed for 17 days. A significant increase in hair growth was observed with 2 and 4% extract. Based on this finding, the optimal dose of the extract for effective hair growth promotion was determined to be 2%. The mechanisms of hair growth promotion were investigated via immunohistochemical analysis of changes in inflammatory cytokines and growth factors in the hair follicles following treatment with 2% extract. The treatment reduced the levels of TNF‑α and IL‑1β, which are pro‑inflammatory cytokines, while it enhanced the levels of IL‑4 and IL‑13, which are anti‑inflammatory cytokines, in the hair follicles. In addition, elevated insulin‑like growth factor I and vascular epidermal growth factor were detected in hair follicles following treatment. Based on these findings, it was suggested that the extract of bark may be utilized for hair loss prevention and/or hair growth promotion.