It is estimated that between 3 and 5 % of the population has AD. We know that the incidence of AD increases with age in childhood. A Danish study of twins between birth and 3 years of age was done in the years 1960-64 and reported a 7% AD incidence. By the year 1991 this figure had increased to 18%. The authors blamed the increase on a closed, indoor climate, outdoor pollutants, an increased exposure to house dust mites, food additives, a decline in breast feeding, and increased parental and physician awareness. Most cases of AD appear before the first year of life, and 90% will develop by the age of 2 years. AD is the most common cause of eczema in children. In general, the incidence of AD is higher in urban than in rural areas, and in families with a history of general atopy or atopic dermatitis.

Racial and Ethnic Variations

There are no consistent findings regarding any racial or ethnic differences in the epidemiology of AD. This may relate to confounding factors associated with differing climates, referral patterns, etc. One study in Britain suggested that the prevalence of eczema increases as socioeconomic class increased.

Genetic Factors

While the genetic susceptibility for atopy has been located on chromosome 11q13 in patients with asthma, no such gene has been found for AD. However, a definite autosomal inheritance pattern has been suggested. Sixty percent of AD patients have family members with the disease. The findings of one study suggested that when both parents had AD, the prevalence in their children was 81%. When one parent had AD and one had respiratory atopy, the prevalence of AD in the children was 59%, and it was 56% when neither parent had AD or respiratory atopy.