NEGATIVIZATION OF PATCH-TESTS TO ALLERGEN S - EXTINCTION OF CONTACT ALLERGY

In an attempt to study the duration of contact sensitivity we reviewed the records of 7 987 patients of the Department of occupational Skin Diseases (Clinique Dermatologique, Hopital Ed.-Herriot), who were patc h tested in the last 15 years. 287 patients with persistent contact de rmatitis were patch tested at least twice. 162 of them had positive pa tch tests to allergens included in the European standard patch test se ries at the first evaluation. 19,2 % of the positive patch test were n egative at retesting several months to 15 years later. Loss of positiv e reactions concerns chiefly borderline irritants: metals, formaldehyd e, fragrance mix and epoxy resin. On the other hand 13 p-phenylenediam ine positive patients invited for re-examination were still patch test positive to PPD despite a job change and discontinuation of contact w ith the allergen ranging from 6 months to 15 years and greater than 5 years in 9 of them. We found no correlation between the patch test neg ativization rate and the period of time between the tests. The loss of patch test responsiveness exclusively to borderline irritants, as wel l as the lack of time dependence, are arguments against the possible e xtinction of the immune response to contact allergens. Our study revea ls a discrepancy between patch test negativization and loss of contact sensitivity.