Aging has been shown to be correlated with the rate and type of contact sensitization, but only a few studies have evaluated patch test reactivity in elderly subjects with an adequately large population.The response patterns to patch testing in 1444 elderly subjects (>65 years) with suspected allergic contact dermatitis were studied, and the results compared with a control group of individuals with suspected allergic contact dermatitis, aged between 20 and 40 years.The prevalence of the positive patch test to at least one hapten was significantly lower in the group of elderly patients compared with adult patients (40.7 vs 47.8%, p<0.0001). However, some allergens, i.e., primin, diaminodiphenylmethane, neomycin, lanolin alcohols, paraben mix, Euxyl K400 and quinoline mix, showed an increased sensitization rate in elderly patients compared with adult patients. These allergens are now less frequently employed in the workplace, or are substances particularly used in the formulation of topical treatment of age-related diseases, i.e., leg ulcer and xerosis. It was also found that the intensity of positive patch test reactions was significantly lower in elderly patients compared with younger subjects, with higher proportions of weak (+) positive reactions. Moreover, elderly patients showed a dynamic pattern of increasing intensity of patch test reactions at the second reading after 3 days compared with the first reading after 2 days more frequently than younger patients (60 vs 53%, p<0.0001).These findings suggest an age-dependent decline of overall positive patch test reactions, but a higher sensitization rate to some allergens frequently used in the composition of topical treatments. The development of an allergic response in elderly patients was found to be delayed, and this may require an additional reading after 7 days and the interpretation of even weak reactions as valid positive patch test reactions.