Platformed care, platformed harm: how social media function as conditional informal infrastructure across eating disorder trajectories among young people in China.

Eating disorders (EDs) among young people in China are rising amid service barriers and stigma, prompting many to rely on social media for interpretation, support, and coping. While existing research often treats social media's influence as static "mixed effects", we reconceptualize social media as conditional informal infrastructure and explore how this infrastructure interacts with users' offline structural scaffolding to shape divergent illness trajectories. We conducted qualitative interviews with 21 young people with EDs, including 5 "dual-role" peer supporters, focusing on their experiences with algorithm-driven platforms (e.g., Xiaohongshu) and super-apps (e.g., WeChat). Through abductive analysis, we identified three analytical segments: (S1) early naming to make distress legible, (S2) constrained navigation for coping resources, and (S3) recovery work to maintain daily routines. Beyond baseline individual traits, outcomes at three critical breakpoints were conditionally shaped by an interactive hierarchy of users' offline scaffolding, including life stressors, social support, stigma, and service barriers. When offline scaffolding was robust, users could bypass digital reliance entirely, or social media facilitated illness validation (S1), routing to bounded support (S2), recovery routine integration and reciprocal care labor (S3). Conversely, when offline scaffolding failed, users relied on symptom-escalation instructions and misleading severity benchmarks (S1), became digitally dependent (S2), and faced recovery scrutiny and systemic overload (S3), triggering stagnation or relapse loops. Overall, platformed care and harm emerge as processual outcomes of offline conditions. Meaningful intervention requires moving beyond content moderation alone to repairing the offline structural deficits that drive young people into digital dependency.