Multiphoton Tomography in Cosmetic Research

Background: Multiphoton tomography (MPT) is a femtosecond laser imaging technique that enables high-resolution virtual biopsies of human skin. It provides a non-invasive method for analyzing cellular metabolism, structural changes, and responses to cosmetic products, providing insights into cell–cosmetic interactions. This review explores the principles, historical development, and key applications of MPT in cosmetic research. Methods: The latest MPT device combines five modalities: (i) two-photon fluorescence: visualizes cells, elastin, and cosmetic ingredients; (ii) second harmonic generation (SHG): maps the collagen network; (iii) fluorescence lifetime imaging (FLIM): differentiates eumelanin from pheomelanin and evaluates the impact of cosmetics on cellular metabolic activity; (iv) reflectance confocal microscopy (RCM): images cell membranes and cosmetic particles; and (v) white LED imaging for dermoscopy. Results: MPT enables in-depth examination of extracellular matrix changes, cellular metabolism, and melanin production. It identifies skin responses to cosmetic products and tracks the intratissue distribution of sunscreen nanoparticles, nano- and microplastics, and other cosmetic components. Quantitative measurements, such as the elastin-to-collagen ratio, provide insights into anti-aging effects. Conclusions: MPT is a powerful in vivo imaging tool for the cosmetic industry. Its superior resolution and metabolic information facilitate the evaluation of product efficacy and support the development of personalized skincare solutions.