First bite syndrome: A systematic review of clinical features and evidence-based diagnostic criteria

First bite syndrome (FBS) is a distinct painful condition. Due to limited recognition and the absence of standardized diagnostic criteria, FBS is frequently misdiagnosed. This study systematically reviews the literature on FBS to comprehensively characterize its clinical presentation and propose evidence-based diagnostic criteria using pooled individual patient-level data.

An exhaustive literature search was conducted in MEDLINE (PubMed), Embase, Web of Science, and CINAHL from database inception to March 1, 2026. Peer-reviewed case reports and case series published in English describing patients of FBS were included. Based on critical appraisal of the literature and pooled individual patient-level data, diagnostic criteria for FBS were developed.

Seventy-one studies comprising 150 individual cases were included. Of these, 56% (84/150) were male, and the mean age was 50.7 ± 15.7 years. The most common precipitating factor was prior surgical intervention. Pain was typically localized in and around parotid region, triggered by the first bite of a meal, and diminished with subsequent mastication. It was most often unilateral, severe, sharp or electric-shock-like, and lasted for seconds. Approximately two-thirds of patients experienced complete resolution, with a median symptom duration of 360 days (interquartile range [IQR] 90-817.5 days).

FBS exhibits a highly consistent and reproducible clinical phenotype. The proposed diagnostic criteria provide an evidence-based framework and may aid recognition of this distinct pain disorder.