Irritable bowel syndrome (IBS) is a disorder of gut-brain interaction characterised by abdominal pain and altered bowel habits. The low fermentable carbohydrate (FODMAP) diet is first-line dietary therapy, yet approximately 50% of patients report insufficient improvement in pain(1). Adverse reactions to histamine, a dietary biogenic amine, are estimated to affect 1 to 3% of the population(2,3), and histamine intolerance has been proposed to cause gastrointestinal and extraintestinal symptoms. However, the evidence for the effects specific to low histamine diets or histamine exposure has not been formally synthesised. This systematic review aimed to evaluate the existing literature on dietary histamine and symptom provocation. Four databases (MEDLINE, CINAHL, Scopus, Web of Science) were searched from inception to June 2026 using a PICO framework: population (humans with gastrointestinal and/or extraintestinal symptoms), intervention (dietary histamine exposure), and outcome (symptom occurrence and severity). Eligible studies included human interventional or observational studies published in English. Screening and full-text assessment were conducted in duplicate via Covidence. Due to high heterogeneity in design, population, dose and outcome measures, meta-analysis was not able to be conducted and findings were synthesised narratively. The search identified 5,043 records across the four databases. Following removal of 1,336 duplicates, 3,707 records were screened, of which 109 were eligible for full-text screening. Following full text review of 50 articles, 11 studies met inclusion criteria and underwent data extraction. These included two randomised controlled trials, one prospective cohort with a blinded challenge, three challenge or provocation studies, one retrospective chart audit, two case reports and two observational studies. Dietary histamine was manipulated in nine studies. No two studies used the same outcome measure. Symptomatic benefit from a low histamine diet was reported in four studies, three of them uncontrolled; two reported mixed findings; two reported symptom aggravation following histamine challenge; and one found no effect. A placebo controlled histamine challenge was used in three studies, including the prospective cohort study. In the largest (n = 59), 62.7% reacted to placebo, and prior improvement on a low histamine diet did not predict the challenge outcome (p = 0.28). The only randomised comparison of a low histamine diet with a histamine rich diet (n = 18, crossover, unblinded) reported lower gastrointestinal pain and skin symptom scores on the low histamine diet (p < 0.05). These preliminary results suggest that the evidence base is small, heterogeneous and dominated by dermatological populations, with gastrointestinal outcomes reported in only three studies. Where blinded challenge was used, the proportion responding was substantially lower than the proportion reporting improvement on open label diet. The findings from this review will inform development of a novel low histamine dietary intervention to test for efficacy in IBS.