Limited research has explored histamine intolerance from the perspective of primary caregivers. Our objective was to develop a practical symptom profile from the standpoint of general practice. We also aimed to gather data on the frequency and timing of disease progression and to establish a staging system. This study utilized a nonrandomized, quasi-experimental design. An in-depth interview was conducted with 217 patients involving 120 questions. To evaluate associations between food intake and symptoms, we recommended either an exclusion diet or a low-histamine diet. A follow-up questionnaire was subsequently administered. We also analyzed 3831 doctor-patient meetings involving upper respiratory symptoms. Symptoms in 77 patients were associated with histamine-rich meals. The most characteristic symptoms included respiratory symptoms (95%), bloating (94%), headache (91%), fatigue (83%), postprandial drowsiness (81%), skin symptoms (81%), diarrhea/loose stool (77%), psychological symptoms (77%), dyspepsia (69%), and muscle/eyelid twitching (61%). Patients with suspected histamine intolerance visited primary care three times more often with upper respiratory symptoms than those without suspected histamine intolerance. The symptom spectrum of histamine intolerance involves multiple organ systems and occurs in distinct, repeating patterns. Symptoms can be described by their duration, sequence, and severity level, which is the key focus of this research, including visual representations. In its most severe stages, histamine intolerance may potentially involve mast cell activation. A personalized diet is associated with a gradual reduction in both the intensity and frequency of symptoms. : The spectrum of histamine intolerance can be characterized by specific symptom patterns with defined frequencies, timelines, and symptom stages.