Multimodal multiphoton tomography in cosmetic research

Over the past two decades, certified multiphoton femtosecond laser tomographs have been used for non-invasive, high-resolution in vivo imaging of human skin by enabling (i) the detection of autofluorescent coenzymes, keratin, melanin, and elastin, (ii) second harmonic generation (SHG) of collagen, and (iii) autofluorescence lifetime imaging. Beyond its application in the detection of malignant melanoma, first MPT studies were focused on evaluating skin modifications induced by the topically applied cosmetic products. Notable applications include assessing long-term anti-ageing effects through changes in the elastin-collagen-ratio, as well as short-term effects by influencing the epidermal NADH level with antioxidants, measured using optical metabolic imaging (OMI). Furthermore, the accumulation sites and penetration depths of ZnO sunscreen nanoparticles and cosmetic microplastics in skin have been investigated. Nowadays, the multimodal ultracompact fiber laser tomograph MPTcompact (Prism Award Winner 2024) that integrates also reflectance confocal microscopy (RCM), is employed by the cosmetic industry in Japan and Europe, providing additional insights into skin health and effectiveness of cosmetic products.