Orthorexia nervosa (ON) – a pathological obsession with healthy eating - is an emerging eating disorder. The precise nature of ON and its causes remain unclear, yet few published research studies speak directly to those with ON tendencies or professionals working with them. Our study redresses this gap in the literature by uncovering the defining ON features and the factors influencing its development. The exploratory qualitative research design included semi-structured interviews with those self-identifying as orthorexic or obsessively preoccupied with healthy eating (n=9); professionals working with ON and eating disorders - psychologists, dieticians and a family therapist (n=7). Data were analysed thematically. ON emerged as multifactorial, with a variety of interrelated influences needing to coalesce for ‘healthy eating’ to become pathological. Key features included rigidity and control (around food choices, routines and preparation) and moral judgements around food, along with a range of negative psychosocial and physical impacts. Influences on the development of ON were organised according to their occurrence at the individual (micro) level, external/relational (meso) level and societal (macro) level. Influences on the individual included health concerns, belief in food as medicine, past trauma, personality (e.g. obsessive, perfectionist), exposure to extreme views and behaviours while growing up and moral concerns. External influences included parents, partners and relational groups (e.g. fitness or clean eating groups). Societal influences included aestheticism, moral citizenship and social media. We conclude that ON is more than an individual pathology, it is symptomatic of our ‘orthorexic society’: where hyper-reflexivity around food choices, conflicting information what is the correct diet, preoccupation with appearance, and emphasis on individual (not collective) responsibility for health combine with individual susceptibilities and ecological/moral concerns, to predispose toward pathological ‘healthy’ eating.