Purpose This study aims to examine how credibility is constructed and negotiated in health-related discourse on Instagram by comparing three distinct influencer profiles − expert, non-expert and patient − and by identifying the epistemic foundations through which each profile is recognized as legitimate within comment-based interactions. Design/methodology/approach Using observational netnography, over 8,000 public comments were collected across three health-related Instagram accounts representing expert, non-expert and patient influencers. A mixed-methods analytical approach combining thematic coding and lexical typology was applied. The analysis draws on source credibility theory alongside health and eHealth literacy frameworks to examine how users evaluate expertise, authenticity and lived experience as distinct credibility resources. Findings Credibility in health-related Instagram discourse emerges through distinct, profile-specific logics of evaluation. Expert influencers are primarily assessed through epistemic authority grounded in clinical legitimacy and evidence-oriented reasoning, though frequently moderated by concerns about commercial intent. Non-expert influencers rely on lifestyle-based credibility rooted in perceived similarity, authenticity, visible outcomes and peer endorsement, reflecting interest-driven and routine-oriented literacy practices. Patient influencers mobilize experiential authority based on lived illness narratives, emotional resonance and community validation, activating forms of experiential literacy unavailable to other profiles. Across profiles, credibility is co-constructed relationally within platform-specific interactional spaces. Research limitations/implications The choice of an expert dentist versus non-expert and patient influencers focused on skincare reduces comparability across cases, and the blurred boundaries between health and wellness content complicate interpretation. Moreover, the absence of demographic data prevents deeper analysis of how literacy varies by user characteristics. Future research could address these limitations by examining multiple platforms, selecting comparable influencer domains (e.g. dermatology) and combining netnography with surveys or interviews to strengthen validity and capture longitudinal dynamics of credibility construction. Practical implications The findings offer guidance for designing digital health communication strategies by identifying which influencer profiles are most effective for evidence delivery, habit formation or community support. Social implications Understanding how credibility is constructed online supports efforts to improve health information quality, reduce misinformation and promote more inclusive health communication practices. Originality/value This study introduces a tripartite framework of health influencer credibility by using observational netnography to compare expert, non-expert and patient influencers within the same social media environment. By analytically distinguishing epistemic authority (experts), lifestyle-based credibility (non-experts) and experiential authority (patients), the study addresses a key limitation of binary expert–lay models, which tend to conflate patients and lifestyle influencers as a single category. In doing so, the paper positions patient influencers as holders of experiential authority, whose lived experience constitutes a distinct source of credibility in digital health communication.
Bayarassou et al. (Mon,) studied this question.