Analysis of the non-immunological activity of allergen extracts in cutaneous tests

The technique proposed by the National Institute for Biological Standards and Control, London (NIBSC, 1977) for the control of allergenic extracts for non-immunological activity in skin tests has proved to be both sensitive and useful. We have observed 'false positive' results to substances such as merthiolate or glycerine and also to lyophilised preparations with sugar, notably glucose, as the carrier substance. Other factors studied in 'false positive' reactions to a given extract were pH, osmotic pressure and the presence of traces of endotoxins or histamine. Individually none of these provided satisfactory explanations for the false positive reactions and the use of antagonists or inhibitors of the release of chemical mediators only confirmed the complexity of the non-immunological reaction and the participation of factors other than histamine.