The case of a very late response to a contact allergen in patch testing

Patch tests (PT) are a significant element of allergological diagnostics. PT are based on the type IV immunological reaction according to Gell and Commbs classification and serve as a diagnostic tool in evaluation of contact skin reactivity. In the Allergic Diseases Diagnostic Centre, Medical University in Poznań, contact allergy is diagnosed by using TROLAB--a standard kit of 23 contact allergens. The allergens are applied on the skin of the interscapular or suprascapular area in Finn Chambers, attached to a hypoallergic plaster. Evaluation of PT results is performed after 48, 72 and even after 96 hrs after application of allergens. The paper describes a case of a very late response to one of contact allergens--paraphenylenediamine (the reaction was observed 15 days after application of patch tests). The precise pathomechanism of this phenomenon, as well as all factors inducing skin reactivity still remain unexplained. Correct instruction of the patient in case of appearance of a very late response to contact allergen will facilitate the diagnostic procedure and will enable correct interpretation of results.