For several decades, the cosmetic preservatives imidazolidinyl urea (IU) and diazolidinyl urea (DU) have not only been poorly characterized but have also had misleading chemical structures assigned to them. The most common trade names of IU and DU are Germall 115 and Germall II, respectively. This publication gives an insight into what these 2 well-known contact allergens consist of and their degradation patterns. Approximately, 30-40% of both products can be characterized by mixtures of allantoin (synthetic starting material), (4-hydroxymethyl-2,5-dioxo-imidazolidin-4-yl)-urea (compound HU) and presumably 1-(3,4-bis-hydroxymethyl-2,5-dioxo-imidazolidin-4-yl)-1,3-bis-hydroxymethyl-urea (compound BHU). A full chemical characterization of compound HU is shown. The remaining part of both IU and DU are believed to be polymers of allantoin-formaldehyde condensation products. The analytical methods used to characterize IU and DU are capillary electrophoresis and nuclear magnetic resonance and mass spectroscopy studies.
It is tacitly assumed that a positive patch test reaction is not affected by adjacent negative tests. However, despite its fundamental importance for the interpretation of test reactions this assumption has not been proven. To test this assumption, special TRUE-test strips were prepared containing placebo, nickel sulphate and fragrance mix as the only allergens, separated by distances of 1 cm and 7 cm and blinded to the investigators. Patients were synchronously tested with two strips. Out of 493 patients tested in 6 centres, the 93 with positive reactions to nickel sulphate only were evaluated. No relevant difference was found between positive nickel reactions in the two different distances to a negative fragrance patch test. We conclude that a positive patch test reaction is not affected by adjacent negative patch tests, which therefore can be neglected for the interpretation of positive reactions.
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