Atopic Dermatitis: Global Epidemiology and Risk Factors
The last few decades have witnessed a considerable increasein atopic diseases, including asthma, allergic rhinitisand atopic dermatitis or eczema according to the newnomenclature, which collectively affect an estimated 20%of the world’s population – particularly children [1–3] .This increase in atopic disorders is not confined to industrializedcountries but also affects developing nations. Atfirst glance, atopic diseases appear to be a group of heterogeneous,unrelated disorders that share some risk factors.Indeed, the complex nature and etiology of these diseaseshave made it difficult to develop a unifying hypothesisto explain their steeply increasing prevalenceworldwide. If two or more allergic diseases (asthma, eczemaand allergic rhinitis) occur within one child, thequestion is whether this occurs purely by chance due tothe high prevalence of these disorders or whether thereare other factors at play. Furthermore, can the presenceof atopy (defined as being positive for a specific IgE) contributeto the excess comorbidity frequently seen withthese conditions? Pooled data from different Europeanbirth cohort studies including data from more than 10,000children with information on underlying diseases andsensitization at 4 and 8 years of age showed that IgE sensitizationis associated with the presence of excess comorbidity,irrespective of preexisting diseases  . However,the level of comorbidity is even higher in children with nosensitization. The authors concluded that the presence ofsensitization accounted for <40% of comorbidity, suggestingthat IgE sensitization can no longer be consideredthe dominating causal mechanism of allergic comorbidity.