The loss of contact sensitization in man.

Little is yet known about the duration of contact sensitivity, but frequent exposure of a target to allergen seems to reduce skin reactivity. The aim of this study was to study the persistence of a specific contact sensitivity in 66 patients with alopecia areata, previously sensitized to DNCB (31 patients) and SADBE (35 patients) between 1978-1985. Patch tests were performed with 0.020 ml of different concentrations of DNCB or SADBE in acetone (0.05%, 0.10%, 0.20%, 1%). The results were read in a standardized manner. Of 66 patients, 47 (71%) had positive reactions and 19 (29%) negative. 8 of the 19 negative patients had been treated with DNCB, 11 with SADBE. Approximately 1/3 of the patients previously sensitized had lost their original sensitivity, and this did not seem to be time-dependent. This phenomenon seemed to be clinically correlated because the majority of the patients were from the "low responders" group. We think that acquired unresponsiveness to topical antigen in man is a possible phenomenon, but that it occurs more rarely than in mice and guinea pigs.