Classification criteria for skin-sensitizing chemicals: a commentary

A formalized, standardized and effective mechanism for the identification of substances which possess significant skin sensitization potential is a necessary first step in the process of limiting the incidence of allergic contact dermatitis. Strategies to achieve such hazard identification are unified throughout the European Union and also have been publicised by the World Health Organization. Global harmonization of these and other approaches (e.g., in the USA) is being driven by the Organization for Economic Cooperation and Development. In this paper, the benefits and limitations of these classification systems are reviewed. A common element of all the systems is that they seek to distinguish important contact allergens from chemicals which are infrequent sensitizers. The European criteria are legal requirements in the EU member states and formal classification as a skin sensitizer leads to mandatory labelling. The most notable omission from current and proposed classification criteria relates to the relative potency of a classified skin sensitizer and the exposure dose. Such information is necessary for proper risk assessment and management measures to be implemented.