One of the major fields of investigation of L'OREAL is to improve the understanding of the chemical composition and structure of skin and hair. To enable a better design of cosmetic products, a thorough understanding of the mechanisms and the nature of the interactions of cosmetic ingredients with these substrates is necessary.Raman is a key analytical method allowing the needed understanding of such mechanisms. In this context,HORIBA Jobin Yvon & L''OREAL Research have established a close collaboration in applying the Raman technique under in vitro conditions or directly in vivo,for hair,skin,nail, eyelashes and model substrates.