Patch test sensitization caused by para-tertiary-butylcatechol. Results of a prospective study with a dilution series

Para-tertiary-butylcatechol (PTBC) has been patch tested in Europe at 1% in petrolatum (pet.) and is now suspected of induction of patch test sensitization. A prospective study was initiated to obtain detailed data on this undesirable risk. A dilution series of PTBC (1%, 0.5%, 0.25%, 0.1% pet.) was used. Patch tests were read on days (D) 1-3, 7, 14 and 21 after application. Patients who were unable to return for late readings were telephoned and asked to report any reaction at the patch test sites. 40 out of 46 patients included completed the study. Patch tests were negative in 35 patients. 4 patients showed a positive patch test at later readings only (D7-D21); 2 patients reacted to a concentration as low as 0.1%. Rechallenge was performed in 2 of these patients, revealing a clearly positive reaction as early as D2 after patch test application. PTBC clearly induced patch test sensitization in 10% of the patients. It cannot be excluded that patch testing with 0.25% PTBC or with even lower concentrations might induce patch test sensitization. The optimal patch test concentration still has to be determined but may be within the range of 0.01% to 0.25% PTBC.