Topical immunotherapy with contact sensitizers: a model to study the natural history of delayed hypersensitivity.

So-called 'topical immunotherapy' (TI) is a well-established treatment modality based on the use of potent contact sensitizers, such as squaric acid dibutylester (SADBE), that are not found in the general or occupational environment of man, and do not induce cross-sensitization to other substances. Thus, unlike patients with sensitivity to other more or less commonplace allergens, subjects submitted to this treatment modality might provide useful data for the study of the natural course of contact sensitivity. On the basis of these premises, we have retrospectively reviewed 40 patients who had consecutively received TI with SADBE for severe alopecia areata and viral warts in the period 1993-2001, and returned to visit after a 1-7-year period since the last therapeutic challenge with the sensitizer. The chronological profile of loss of contact sensitization of this case cohort has been evaluated and compared to that of other series available in the literature. Provided more standardized TI application procedures are established, aim-oriented studies of the outcome of this treatment modality may bring useful data to be employed in construction of predictive models of decay of contact sensitization under conditions of antigen avoidance.