Asthma is the commonest chronic condition of childhood. Children with asthma in the UK have the worst outcomes across Europe and other high-income countries. There are significant socioeconomic inequalities that impact the prevalence and outcomes of asthma (emergency healthcare utilisation, hospitalisation, critical care admission, mortality and quality of life). In this review we discuss these inequalities and the underlying mechanistic links, using the UK as an example of how poverty in a high-income country results in inequality in asthma outcomes. These inequalities and underlying mechanisms need to be understood by clinicians, policymakers and wider stakeholders to be redressed such that avoidable harm and asthma deaths in children can be prevented.