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Asthma can no longer be regarded as a single disease but one of multiple subtypes.The limited success of targeting Th2 cytokines has led to a search for new networks.Exposure microbial products in early life protects against asthma.Once asthma is established danger signals enhance allergen sensitisation and inflammation.The epithelium is at the centre of asthma through re-engagement of foetal pathways.Asthma is an inflammatory disorder of the conducting airways that has traditionally been classified according to severity. While this has been helpful in guiding treatment with drugs that are currently available such as β2-adrenoceptor agonists and corticosteroids, it takes little account of disease heterogeneity and causal pathways. This review draws attention to subphenotypes of asthma involving different mechanisms and moves the focus away from the adaptive immune response more towards innate immune mechanisms. This mandates a new view of the disease in which causal pathways linked to biomarkers are found and treatments targeted to these pathways as described in a more personalised approach to medicine.