Winfried Steiling

Up to today, product safety evaluation in the EU is predominantly based on data/information on their individual ingredients. Consequently, the quality and reliability of individual ingredient data is of vital interest. In this context, the knowledge about skin sensitization potential is an explicit need for both hazard and risk assessment. Proper skin sensitization data of the individual chemicals is essential, especially when dermal contact is intended, like for cosmetics. In some cases, e.g., in the presence of irritating chemicals, the combination of individual ingredients may also need to be evaluated to cover possible mixture effects. Today, it seems unlikely or even impossible that skin sensitization in humans can be adequately described by a single test result or even by a simple combination of a few data points (in vivo or in vitro). It is becoming evident that a set of data (including human data and market data) and knowledge about the ingredient’s specific sensitizing potency needs to be taken into account to enable a reliable assessment of skin sensitization. A more in-depth understanding on mechanistic details of the Adverse-Outcome-Pathway of skin sensitization could contribute key data for a robust conclusion on skin sensitization.

An in vitro technique for the prediction of percutaneous penetration/dermal absorption is recommended by the European SCCNFP (The Scientific Committee on Cosmetic Products and Non-Food Products intended for consumers) for the safety evaluation of particular ingredients. In 2002, this in vitro method became officially accepted at the OECD level and will be published as OECD Guideline 428. Examples are given for its routine application, demonstrating the bioavailability of cationic azo hair dyes out of an aqueous solution compared to data from a realistic standard hair dye formulation. Data from two direct hair dyes, BASIC BROWN 17 and BASIC YELLOW 57, demonstrate the results of applying this new in vitro technique without radiolabelled material. Direct hair dyes are frequently used in semi-permanent cosmetic hair colourations without the additional need for hydrogen peroxide. In the light of the in-house experience over about 5 years in using excised pig skin for measurements of the percutaneous penetration and dermal absorption of hair dyes, the technique was found to be successful and appropriate for reducing the number of test animals normally used for toxicological assessments.