Background: Food hypersensitivity is often self-diagnosed, and research into barriers to help-seeking is scarce. Aims: This study in the United Kingdom sought to establish the relationship between health beliefs, health anxiety, and diagnostic type (medically diagnosed vs. self-diagnosed) in individuals with food hypersensitivity, and qualitatively explored attitudes of self-diagnosed individuals and their barriers to attaining a medical diagnosis. Method: A mixed-methods design involving 107 participants with food hypersensitivity (64 medically diagnosed and 43 self-diagnosed). Participants completed an adapted version of the health belief model questionnaire and a health anxiety questionnaire. A subset of six self-diagnosed participants took part in semi-structured interviews. Results: Binary logistic regression showed that health anxiety, perceived susceptibility, and perceived severity were significantly associated with diagnostic type. Qualitative thematic analysis of interviews yielded three themes: control over food, diagnosis, and treatment; judgment regarding feeling judged negatively on one’s choice of food, and being compared to fad-dieters; and the public’s and participants’ own lack of perceived severity of food hypersensitivity. Limitation: The sample was self-selected and therefore not necessarily representative of the population; however, an adult population was examined in an area that has so far largely studied children. Conclusion: Health psychologists should become involved in developing and testing interventions to help those with food hypersensitivity to control and reduce distress. Further researching the issues of control, judgment, and perceived severity could help tackle barriers to help-seeking behavior.