Abstract
Natural ingredients with soothing and skin-protecting effects are becoming increasingly popular in cosmetic science. Great interest has been directed to birch sap, a nutrient-rich fluid from Betula species. This study aimed to investigate whether birch sap can modulate inflammatory responses and maintain skin barrier functions in both cell and animal models. The polysaccharide composition of birch sap was characterized. TNF-α/IFN-γ-stimulated HaCaT keratinocytes were used to assess the effects of birch sap on inflammatory cytokine expression and activation of MAPK and NF-κB signaling pathways. An in vivo model of chemically induced skin irritation was further used to examine the effects of oral birch sap administration on skin hydration, transepidermal water loss, histological features, and cutaneous blood flow. Birch sap significantly reduced IL-1β, IL-6, and IL-8 expression and attenuated MAPK and NF-κB phosphorylation. In vivo, birch sap improved hydration, reduced transepidermal water loss, epidermal thickening and erythema, and decreased elevated skin blood flow associated with inflammation. These results demonstrate that birch sap provides modulatory effects on inflammation and barrier-supportive effects in both cellular and animal models, suggesting its potential as a naturally derived cosmetic ingredient for promoting skin comfort and maintaining epidermal barrier integrity.