**1.2 Diagnostic criteria of AD**

During the past decades about 10 diagnostic criteria for AD have been set up(Brenninkmeijer et al., 2008),while the Hanifin and Rajka diagnostic criteria(in 1980) and Williams diagnostic criteria(in 1994) are the two most widely used methods in the world(Roguedas et al., 2004).The H-R criteria is such a detailed one (4 major and 23 minor criteria) that it is time consuming and not easy to operate, and thus mainly suitable for investigative studies and impractical for epidemiologic studies. What's more, some of the minor features described in the criteria, such as anterior neck folds and the Dennie-Morgan infra-orbital fold, has been challenged for their diagnostic significance in a study on Swiss AD (Mevorah et al., 1988). The concise Williams criteria (1 mandatory and 5 major criteria), are suitable for clinical and epidemiological studies. Williams criteria has been extensively validated(Brenninkmeijer et al., 2008). Due to its inherent nature of easy operation, this diagnostic criterion could be recommended in future international studies. In 1995, International Study of Asthma and Allergies in Childhood (ISAAC) set up ISAAC questionnaire for prevalence survey of childhood AD(Asher et al., 1995).Taken together, an ideal diagnostic criteria need to be well-validated ,easy to apply and suitable for interventional multicenter trials.
