Thresholds in contact sensitization: Immunologic mechanisms and experimental evidence in humans - an overview

The evidence from practical experience in man, from controlled human testin g and from both chemical and biological mechanistic considerations, demonst rates that the thresholds for skin sensitization exist both at the level of induction as well as sensitization. For a given contact allergen, the conc entration (expressed in dose per unit area), which is at the threshold, has to be defined in terms of the nature and extent of the skin contact involv ed, and whether it is the induction of skin sensitization or its elicitatio n that is involved, since the numerical values will depend heavily on these parameters. The induction and elicitation of contact allergy is influenced by several factors: the total dose of the allergen, its surface concentrat ion, the size of area over which it is applied, antigenic potency of the su bstance, number of exposures, anatomical site of exposure, effect of draini ng lymph nodes, matrix (vehicle) of allergen, effect of occlusion, degree o f percutaneous penetration, effect of diseased skin/trauma and possibly a h ost of other, as yet unknown, variables. (C) 2001 Elsevier Science Ltd. All rights reserved.