Imaging analysis of cosmetic ingredients interacted with human hair using TOF‐SIMS

Human hair damage is caused by chemical treatments and various daily factors. A number of cosmetic ingredients have been developed to repair hair damage. It is important to know the localization of cosmetic ingredients distributed on human hair to understand the interaction mechanism of these ingredients with the hair. In this work, the distribution of cosmetic ingredients on damaged hair was investigated using time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS). We examined the penetration of L‐theanine and the adsorption of cationic chitosan. The TOF‐SIMS imaging analysis revealed that L‐theanine penetrated deep and was distributed uniformly inside the damaged hair. Further, cationic chitosan was uniformly adsorbed on the hair surface. The analysis results showed that TOF‐SIMS is one of the most convenient methods to estimate the distribution of cosmetic ingredients on the hair.