Regulatory classification of substances oxidized to skin sensitizers on exposure to air

Regulatory classification of substances in the European Union (EU) is inten ded to identify their hazardous toxicological properties in a formal and ha rmonized manner. In the regulatory work, a specific chemical with its molec ular structure is classified as a skin sensitizer. This implies that the co mpound is stable throughout its lifetime. The purpose of the present paper is to discuss the problem of skin sensitizing oxidation/degradation product s formed by air exposure of various materials or substances with very low a llergenic activity. In regulatory classification work on skin sensitizers, the intrinsic suspectibility of a chemical to air oxidation (autoxidation) should be taken into consideration. We give examples of natural terpenoid m aterials, but the concept of allergens formed by air oxidation can apply to Other materials widely used in industrial products. If a positive classifi cation is made for a substance with a known chemical structure, a note shou ld indicate that the primary chemical structure of the notified substance i s not a skin sensitizer, but that (some of) its oxidation products are. Com plex mixtures which inevitably contain sensitizing oxidation products shoul d (on the basis of sufficient evidence) be classified as skin sensitizing.