Dysregulation of the immune defence system of the lungs can induce inflammation and lead to chronic respiratory diseases, such as chronic obstructive pulmonary disease or asthma. Numerous cytokines are involved in this process. Among these cytokines, those of the interleukin 6 (IL-6) family play a very important immunoregulatory role. Recent studies on IL-6 have shown that this cytokine is not simply a by-product of inflammation, but instead may play a role in the aetiology of asthma. It has been suggested that a deeper understanding of the molecular mechanisms and pathways related to IL-6 could improve asthma treatment while minimising side effects. A few genetic studies have already reported an association between IL-6 genetic variants and asthma, with divergent results depending on the type of asthma. Specifically, a Finnish study showed an association with adult-onset allergic asthma, while a GWAS study showed an association specifically with childhood-onset asthma and no association with adult-onset asthma. The association between IL-6 and asthma seems to be established, but not yet well understood, especially regarding to which asthma phenotype the cytokine may be related. Furthermore, interactions between IL-6 and tobacco smoking exposure were shown in different diseases including asthma.