The frequency of contact allergy in atopic patients with dermatitis.

A prospective study was performed to establish the frequency of contact allergy in atopic patients presenting with dermatitis, compared with non-atopics suffering from dermatitis. During 1987-1988, all new patients aged 15 years or older, who consulted us for dermatitis, were investigated. They were patch tested with the European standard series, methyl(chloro)isothiazolinone and other relevant allergens. In addition, they were prick tested with 24 inhalant and 11 food allergens. Patients having at least 2 positive prick tests, and patients with 1 positive prick test and a (family) history of atopic diseases were defined as atopics, as were those who presented with classic atopic dermatitis but with negative prick tests. 499 patients were evaluated: 159 men and 340 women. 214 patients (43%) were atopic, the other 285 (57%) were non-atopic. In the atopic group, 79 persons (37%) had at least 1 positive patch test reaction. In the group of non-atopics, 149 patients (52%) had contact allergies. The difference is statistically significant (chi 2; p less than 0.05). It is concluded that adult atopics seen in dermatological practice who present with dermatitis are less frequently contact sensitized than such patients who are non-atopic. Nevertheless, a yield of nearly 40% positive patch test reactions in this group still makes routine patch testing necessary.