BackgroundChildhood eczema is often poorly controlled owing to underuse of emollients and topical corticosteroids (TCS). Parents/carers report practical and psychosocial barriers to managing their child’s eczema, including child resistance. Online interventions could potentially support parents/carers; however, rigorous research developing such interventions has been limited.AimTo develop an online behavioural intervention to help parents/carers manage and co-manage their child’s eczema.Design and settingIntervention development using a theory-, evidence-, and person-based approach (PBA) with qualitative research.MethodA systematic review and qualitative synthesis of studies (n = 32) and interviews with parents/carers (n = 30) were used to identify barriers and facilitators to effective eczema management, and a prototype intervention was developed. Think-aloud interviews with parents/carers (n = 25) were then used to optimise the intervention to increase its acceptability and feasibility.ResultsQualitative research identified that parents/carers had concerns about using emollients and TCS, incomplete knowledge and skills around managing eczema, and reluctance to transitioning to co-managing eczema with their child. Think-aloud interviews highlighted that, while experienced parents/carers felt they knew how to manage eczema, some information about how to use treatments was still new. Techniques for addressing barriers included providing a rationale explaining how emollients and TCS work, demonstrating how to use treatments, and highlighting that the intervention provided new, up-to-date information.ConclusionParents/carers need support in effectively managing and co-managing their child’s eczema. The key output of this research is Eczema Care Online for Families, an online intervention for parents/carers of children with eczema, which is being evaluated in a randomised trial.