Why is atopic dermatitis becoming more common?

The prevalence of atopic dermatitis in six- and seven-year-old children varies from less than 2% in Iran and China to 10% to 20% in the United States, United Kingdom, Australia, and Scandinavia. The incidence was only 2% in those born before 1960. The increase over time and difference between more- and less-developed nations has been explained by the “hygiene hypothesis.” This postulates that a reduction in the frequency of childhood infections results in an increased incidence of various allergic and autoimmune diseases including atopic dermatitis, asthma, allergic rhinitis, childhood insulin-dependent diabetes mellitus, and Crohn’s disease.