Insights from Biophotonic Imaging and Biochemical Analysis on Cellular and Molecular Alterations Exhibited in Dull Skin

Dullness or lack of radiance in facial appearance is a common concern among females. Previous studies have linked skin dullness to aging and revealed alterations in skin pigments. However, younger individuals (ages ≤ 35) also report concerns about dull skin in their hectic daily lives, which may not involve pigmentation changes. We hypothesized that the mechanisms underlying dullness in youth differ from those associated with aging. To investigate this, we measured cellular and molecular changes in 132 healthy Japanese and Chinese females aged 18 to 35 using biophotonic multiphoton tomography and biochemical tape-strip analysis. Our findings revealed that dull skin exhibited a thicker stratum granulosum and less densely packed keratinocytes in deeper layers. Biochemical analysis showed upregulation of interleukin-36γ and downregulation of E-cadherin in dull skin, with interleukin-36γ levels negatively correlating (p = 0.023) with metabolites of filaggrin. These alterations resemble those observed in inflammatory skin conditions, suggesting an additional mechanism of skin dullness beyond pigmentation. In vitro cultured cell models evaluated the efficacy of three skincare ingredients: galactomyces fermentation filtrate, bisabolol, and batyl alcohol. Galactomyces suppressed interleukin-36γ (p = 0.037), while both batyl alcohol (p = 0.006) and bisabolol (p = 0.049) showed beneficial effects on filaggrin. Targeting these biomarkers may improve the appearance of dull skin.