Aim: To co-develop Caregiver Reported Outcome Domains (CRODs) towards a core outcome set (COS) for ichthyosis in clinical practice and service delivery. Background: Ichthyoses is an umbrella term for a group of over 20 rare, chronic, inflammatory skin diseases characterised by thickened, scaling and dry skin. It is a highly visual, life-limiting, incurable, often fatal disease, for which there is limited healthcare knowledge and few treatment options available to caregivers. Research emphasises that ichthyoses can exert a substantial burden of care, potentially impacting the quality of life for both those affected and their caregivers. Dermatology Life Quality Index (DLQI) scores place ichthyoses among the skin disorders with the most harmful impact on a patient's quality of life. Without curative intervention, the mainstay of life-long symptom management often remains the responsibility of the caregiver, often assuming nursing roles without prior training or appropriate information. Despite the known negative impacts on families and other informal caregivers, there are no robust, co-designed instruments to measure the needs of this population. This Core Outcome Set (COS) aimed to inform the development of appropriate ichthyosis caregiver outcome measurement and improve COS uptake. This COS uniquely invited experts by experience (caregivers and multi-disciplinary professional experts) to prospectively collaborate to co-develop a minimum set of caregiver reported outcome domains (CRODs) that measure relevant and suitable concepts of ichthyosis for clinical practice, service delivery and research. To promote content validity and improve rigour, outcome domains were identified using a hybrid of literature and qualitative feedback from ichthyosis caregivers. Consensus on the most important outcome domains was achieved using an international e-Delphi study, online anonymous qualitative feedback, statistical testing of the e-Delphi results and an online consensus discussion. Method: A sequential mixed method design, using a two-staged approach, was used to address the research question. The protocol for this COS evolved using public and patient involvement (PPI). An international multi-disciplinary expert group included clinical experts, patient caregivers, support group representatives, policy makers, researchers and service providers were recruited at the outset. Experts by experience, or caregivers, were recruited through medically recognised online international ichthyosis support groups. Stage 1: Item generation: I conducted a comprehensive systematic literature review to identify available psychosocial needs assessment tools, validated for use with caregivers of paediatric patients with dermatologic disease (registered on PROSPERO). Then, I carried out an international multi-method qualitative study using framework analysis with 39 caregivers across 4 continents. Stage 2: Item refinement: I undertook an international e-Delphi study approach involving international multi-disciplinary experts, and caregiver groups. The expert groups were asked to rate the importance of candidate outcome domains, and then the helpfulness of respective supports. Preliminary psychometric evaluation of the needs assessment tool for ichthyosis caregivers (NAT-IC) was also conduced. Analysis: In-depth interviews of caregivers were transcribed and explored using a thematic analysis. Qualitative feedback from expert groups were itemised for use in the scale development. I undertook inter-rater reliability between the professional and caregiver expert groups and psychometric analyses on the different subsections of the NAT-IC. Results: Study 1: Very few needs assessment tools were validated for use among caregivers of paediatric patients living with dermatologic disease. Ten disease-specific assessment tools and one dermatology-specific assessment tool were identified. With the exception of three domains (emotional, social and financial), none of the other twenty-eight domains identified in this review were reported in more than one tool. None of the included tools were available as a caregiver self-report e-tool, allowed for caregiver assessment of disease severity and/or flagging of caregiver vulnerability. The lack of caregiver assessment application in healthcare settings may be explained by poor content validity, the biomedical model of assessment reflected in existing tools, and/or the poor methodological properties of the included tools. Study 2: As the largest international qualitative study to explore the lived experience of ichthyosis caregivers to date, this study identified an entire constellation of supportive care needs, relevant along the entire care continuum for a representative group of caregivers and patients. Although the study confirmed the presence of the three most frequently reported outcome domains in the systematic review, this study led to the development of an additional fifteen meaningful outcome domains. Outcome domains were generated from the presence of supportive care needs arising from two overarching, yet often competing, themes relating to the provision of appropriate care for their affected child and addressing their own personal needs. Core areas of supportive care needs included: (i) information support (disease and care specific information, financial matters, practical supports, genetic diagnosis and counselling) (ii) education and training (formal disease recognition at national level, caregiver (self) identification, management of the psychosocial impact of ichthyosis on both the patient and caregiver, importance of positive language, appropriate healthcare expertise and effective communication) (iii) formal support (healthcare access, caregiver needs assessment, service delivery, formal disease recognition, shared-decision making, communication pathways, engagement with education and childcare sectors, relationships with healthcare professionals) (iv) informal support (social support networks including peer, family, online and societal) (v) physical health (vi) emotional health and (vii) the need to manage their own lives. When caregivers perceived a gap in the provision of healthcare and social care support, emotional distress was intensely amplified. This is the first qualitative study to propose a conceptual framework relating to the supportive care needs on the ichthyosis care continuum, with findings suggesting that the modification of any one element in our framework (demands and resources), through feedback loops, may result in a different bi-directional psychosocial impact for both the caregiver and the child. Additionally, key transition stages, positives of caregiving, coping strategies, helpful dermatological supports, impactful disease parameters and influencing factors potentially associated with severity and/or caregiver need were identified and may prove useful for understanding the triggers and barriers within the caregiver/healthcare dyad. Study 3. No significant difference was found between any of the severity groups (mild/ moderate/severe) and total need, implying that all caregivers of children living with ichthyosis should have their needs assessed in a timely and appropriate manner. The NAT-IC is the first comprehensive, online, self-report solution-focused model of dermatological caregiver assessment that can be used to directly assess unmet ichthyosis caregiver needs at both the problem and support level throughout the care continuum. The finalised NAT-IC contains seventeen 'core' outcome domains and is the first dermatological caregiver assessment to include a caregiver self-report perceived severity scale of impactful disease parameters (SPIS) as well as a screening section. Preliminary psychometric evaluation of the NAT-IC suggests a valid and reliable needs assessment e-tool that includes outcome domains that achieved positive consensus in the e-Delphi study and/or were significantly associated with a total severity and/or need score.