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Skin is the largest organ of the body and its function is not limited to a physical barrier.According to the total skin surface area (about 2 square meters, 15% of the body weight) it can be also considered as one of the main extra-hepatic metabolism organs for endogenous compounds and xenobiotics.Thus, the research on skin metabolism would require a real scientific effort and dynamism to characterize skin metabolizing enzymes and their activities.The limited and variable availability of fresh normal human skin (hereafter referred to as NHS) has resulted in the development of sophisticated biological tools such as reconstructed human skin models (hereafter referred to as skin models), such as those from SkinEthicTM laboratories.As well new European policy banning the use of animal testing (7th European amendment to the cosmetic directive) has led the cosmetics industry to focus on in vitro alternative methods to animal experimentation increasing the need of skin models.L'Oreal uses these skin models daily to develop new cosmetic ingredients.Consequently, assessing and comparing some of these skin models (EpiskinTM, SkinEthic RHETM and the full thickness model of SkinEthicTM) with NHS in terms of metabolic equipment and capability was essential in order to be confident in their use.We developed an approach to characterize the skin metabolic capabilities build on two steps.At first, the gene expression study by RT-PCR to assure the presence of the main enzymes mRNA.However, the presence of mRNA material is not necessarily proof that the protein is present and/or catalytically active.Consequently, the second step was the metabolizing enzymes activities characterization using specific substrates.This work shows the presence of the main cutaneous isoforms of cytochromes P450 (CYP,1A1/1B1, 2B6/2C18/2E1, 3A5/3A7A1 and 9A1), esterase (AADAC, CEL, ESD, CES1/2 and PLA2G4B), alcohol dehydrogenase (ADH, 1B, 7), aldehyde dehydrogenase (ALDH, 1A family, 2,3A/3B family, 4A1, 5A1,6A1,7A1), peroxydase (GPx, 1,2, 3, and 4;PTGS1 and PTGS2), glutathione-S-transferase (GST, A, M, P, T), N-acetyl transferase(NAT1 and NAT5), uridinyl diphosphate glucuronyl transferase (UDPGT, 1A family) and sulfotransferase (SULT, 1A1, 1E1 and 2B1).