Experimental and computational investigation of collagen modification in skin chromatic alterations

Skin darkening and yellowing are significant concerns associated with aging, particularly among Asian women. Skin sallowness in aging is influenced by factors such as melanin deposition, dermal glycation, and carbonylation, which alter skin’s optical properties. However, the mechanisms by which glycated/carbonylated dermal collagen contribute to skin sallowness remain poorly understood. In this study, the absorption coefficients of melanin, glycated-collagen (GC), and carbonylated-collagen (CC) were measured, and light reflection, transmission, absorption, and scattering in the epidermis and dermis with varying chromophores were analyzed using Monte Carlo simulation on an eight-layered skin model. While all chromophores contribute to skin darkening (resulting in decreased L * values) and yellowing (indicated by increasing b * values), the mechanisms of how each chromophore impact skin yellowness is distinct. When the volume fractions of melanosome increased from 0.067 to 0.175, the b * value of epidermal reflected light decreased by 29.18%, whereas that of dermal reflected light increased by 38.39%, indicating that melanin primarily enhances the reflection of yellow light from the epidermis. For GC and CC, reducing the Rayleigh scattering fraction from 0.7 to 0.2 led to a 22.85% increase in the yellowness of total reflected light. GC and CC enhance the backscattering of yellow light by modifying dermal scattering properties, thereby increasing the yellowness of dermal reflected light. Our study provides a comprehensive optical analysis of the chromatic characteristics of skin chromophores and offers new insights into how they impact skin color. These findings contribute to a better understanding of skin aging and pave the way for developing targeted interventions to address skin darkening and yellowing concerns.