Background: Atopic dermatitis is a common multifactorial disease that seems to be increasing in frequency.
Objective: Our purpose was to evaluate and expand previous findings on the incidence of atopic dermatitis and its concordance rates in twins.
Methods: A mailed questionnaire study was conducted. It involved 812 twin pairs living in Fyn County, Denmark, as of Jan. 1, 1987 and born between 1965 and 1979. Zygosity was determined by the similarity method.
Results: The response rate was 92%. The cumulative incidence rate (up to 7 years) of atopic dermatitis increased significantly from 0.06 for the birth cohort 1965-1969 to 0.12 for the birth cohort 1975-1979. The pairwise concordance rate was 0.72 in monozygotic and 0.23 in dizygotic twin pairs.
Conclusion: The frequency of atopic dermatitis is still increasing but not as rapidly as in the 1960s. The magnitude of the concordance rates indicates that genetic factors are decisive in the development of atopic dermatitis. It is suggested that widespread environmental factors are operating in genetically susceptible persons.