Information on sex, season of birth, death, emigration, parental identity, sibling's identity and exact address will be obtained from the Danish Civil Registration System. The investigators will use information on parental identity to link every child to its parents and obtain information on parents' origin of birth, single parenthood and the number of children in the household. The investigators will furthermore derive information on population density based on information on the municipality in which the child lives. Information on parental and sibling's identity will be used to link information on family history of atopic dermatitis to the child. Atopic dermatitis is categorized according to the algorithm described in detail under "9. Outcome measures".