BACKGROUND: Studies of incidence of contact allergy in a general population have not been reported. Data from incidence studies may support and direct strategies for prevention of contact allergy and allergic contact dermatitis.

OBJECTIVE: To study the incidence of contact allergy and evaluate risk factors for developing contact allergy in an adult general population sample.

PATIENTS AND METHODS: In 1990 a random sample of 567 persons of the 15-69-year-old population living in the western part of Copenhagen County (Denmark) was patch tested in a cross-sectional study. In 1998 a follow-up study was performed. Of 540 invited, 365 (68%) were patch tested again.

RESULTS: In the follow-up study, 37 persons (12%) of the 313 patch-test-negative persons in 1990 had developed one or more positive patch tests (incident contact allergy). Twenty cases (6%) of incident nickel allergy and 25 cases (8%) of incident contact allergy to one or more haptens other than nickel were found. The data indicate that female sex, young age and ear piercing (before 1990) were risk factors for developing nickel allergy. Between 1990 and 1998 metal contact dermatitis was reported in seven women with incident nickel allergy. Six of these women had bought the eliciting item in Denmark before 1995, when vigorous control of the Danish nickel legislation was introduced.

CONCLUSIONS: We found a considerable number of incident cases of contact allergy in the adult population. The results of the study support the actions taken to restrict the use of the allergens most frequently encountered, and to increase the labelling demands to products intended for prolonged contact with the skin or a combined action.