Asthma is a complex disorder and evidence now suggests that it is not solely attributable either to allergy or eosinophilia. Non-eosinophilic asthma accounts for up to one half of all cases and a large proportion have a non-allergic aetiology. The innate immune system responds to a variety of triggers, including viral and bacterial components which are known non-allergic triggers of asthma. The innate immune response may be involved in both the development of and protection against asthma. Factors which are likely to determine the nature of the response include the timing of the exposure (childhood or adulthood), baseline asthma inflammatory subtype (eosinophilic or non-eosinophilic) and the dose of the exposure. Gene–environment interactions are likely to modify the response. Further research is required to elucidate the specific mechanisms involved in the innate immune response in asthma and will be important in the identification of new targets for therapy and management.