Rare allergens - hidden sources of allergens.

Acceleration of technical development results in growing difficulties to trace allergens. In this respect rare allergens as well as hidden sources of well-known allergens not infrequently cause persistence of allergic dermatitis. Examples are presented for di-ethyl-ester of maleic acid, hydroxylammoniumhydrochloride, N-methyl-p-aminophenol, 2-hydroxy-3-naphtoic acid o-aniside and N-acetoacetyl-benzylamide.