Another look at seasonal variation in patch test results - A multifactorial analysis of surveillance data of the IVDK

There is conflicting evidence concerning seasonal variability of patch test results and no evidence concerning the influence of season on weak-positiv e, possibly false-positive, irritant reactions, which was analysed in the p resent study. Data collected in the German Information Network of Departmen ts of Dermatology (IVDK) 1992 to 1997 were combined with external environme ntal data on temperature and absolute humidity in Germany, and bivariate as well as logistic regression analyses performed concerning the association between reactivity to selected allergens and air temperature and absolute h umidity on the respective days of patch testing. Between 39,239 and 41,629 patients had been tested with the 4 allergens considered here. Only formald ehyde exhibited a distinct increase in questionable or irritant as well as weak-positive reactions associated with dry, cold weather. Methylchlorosiot hiazolinone/methylisothiazolinone and lanolin alcohol showed only a weak, a nd epoxy resin no, association with climatic conditions. The results indica te that weak-positive reactions, at least to formaldehyde as a prototype of an allergen which is at the same time a marginal irritant, may sometimes b e irritant rather than allergic. Patients showing these should be re-tested to improve the poor reproducibility observed with this allergen.