Ingredients Tracking of Cosmetic Formulations in the Skin: A Confocal Raman Microscopy Investigation

Abstract : Confocal Raman microspectroscopy (CRM) was used to follow the absorption of retinol into the skin and to track the absorption of ingredients in topically applied formulations. Three surfactants, PEG20C12, PEG20C18:1 (hydrophilic) and PEG6C18:1 (lipophilic), were used in preparing three o/w emulsions and three surfactant solutions all containing retinol. Quantitative retinol penetration studies for 24 h were carried out using Franz diffusion cells. CRM was used to follow the skin penetration of retinol, oil and water and also to study a possible modification of the lipid skin barrier in the stratum corneum (SC) using the ratio of I(2880)/I(2850). The oily surfactant solution containing PEG6C18:1 and dodecane showed the highest retinol penetration rate. This appears to be related both to the short polar head group of the surfactant and to the effect of dodecane on skin lipids. All the surfactant solutions showed a higher penetration rate compared with the corresponding emulsions. CRM measurements showed that the ratios of I(2880)/I(2850) were significantly modified using surfactant solutions. Penetration behavior appeared to be dependent on the surfactant used in the formulation. CRM associated to the Franz cell method gives new insights on permeation of drug related to vehicle or ingredients