In order to understand the mechanisms of the functions of a cosmetic ingredient, it is important to know the distribution of its agents in the epidermis of the skin. Imaging analysis of these agents by microscopic methods are quite difficult, and only a few studies have been reported to date. We analyzed the penetration of cosmetic ingredients into the skin using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Pig skin treated with a cosmetic preparation was used as a model for the human epidermis. The sample was embedded in resin or glue and cross-sections were carefully cut using an ultramicrotome. After the appropriate sample preparation methods were determined, the synthetic pseudoceramides contained in the cosmetic preparation were detected as individual molecular ion peaks and it was revealed that these agents are able to penetrate the stratum corneum tissue. TOF-SIMS analysis detects these agents as separated masses and it is thus considered to be one of the most versatile methods of high resolution imaging analysis of such species. (c) 2006 Elsevier B.V. All rights reserved.