Studies on percutaneous penetration are needed to assess the hazards after unintended occupational skin exposures to industrial products as well as the efficacy after intended consumer exposure to topically applied medicinal or cosmetic products. During recent decades, a number of methods have been developed to replace methods involving experimental animals. The results obtained from these methods are decided not only by the chemical or product tested, but to a significant degree also by the experimental set-up and decisions made by the investigator during the planning phase. The present MiniReview discusses some of the existing and well-known experimental in vitro and in vivo methods for studies of percutaneous penetration together with some more recent and promising methods. After this, some considerations and recommendations about advantages and limitations of the different methods and their relevance for the prediction of percutaneous penetration are given. Which method to prefer will depend on the product to be tested and the question asked. Regulatory guidelines exist for studies on percutaneous penetration, but researchers as well as regulatory bodies need to pay specific attention to the vehicles and solvents used in donor and sampling fluids so that it reflects in-use conditions as closely as possible. Based on available experimental data, mathematical models have been developed to aid predictions of skin penetration. The authors question the general use of the present mathematical models in hazard assessment, as they seem to ignore outliers among chemicals as well as the heterogeneity of skin barrier properties and skin conditions within the exposed populations. This MiniReview will discuss some of the existing and wellknown experimental in vitro and in vivo models together with some more recent and promising models and give some considerations and recommendations about advantages and limitations of the various models and their relevance for predictions of percutaneous penetration. An overview of the methodologies discussed can be found in table 1.Dermal exposure may be unintentional after environmental or occupational exposure or intentional after the use of topically applied medication or use of cosmetic products. In all cases, the assessment of the potential for percutaneous penetration or temporary deposition within the skin is an essential element in assessing risk as well as efficacy after dermal exposures.Decades of preventive efforts have decreased the inhalational exposures at work places. At the same time, topically applied pharmaceuticals are being used ever more often. Together, this has increased the relative importance of dermal exposures.Knowledge concerning percutaneous penetration and the potential to reach target sites closes the gap from exposure assessment and hazard identification to risk assessment. If a substance is unable to penetrate the stratum corneum (SC) or affect the skin barrier function in any way, then the need for further assessment of risk becomes less evide...