An European Union (EU) report on fragrance allergens in cosmetic products has advised that compounds suspected to act as “prehaptens and/or prohaptens” should be considered allergens, unless it can be demonstrated they are safe for consumers. The study by the EU scientific committee on consumer safety says that they can become especially allergenic through abiotic and metabolic reactions.
Fragrance substances known to be prehaptens forming sensitising compounds by air oxidation include limonene, linalool, and linalyl acetate. And those known to be prohaptens, which form sensitising compounds by metabolic transformation include cinnamyl alcohol, eugenol, isoeugenol and isoeugenol