Soy sauce has very high histamine levels because of its long fermentation process — dark soy sauce can contain nearly 478 mg/kg of histamine, well above the thresholds that cause symptoms in histamine-sensitive people. It also contains tyramine (another biogenic amine that competes with histamine for the same breakdown enzyme, making both more potent). On top of the histamine issue, soy sauce is made from both soy and wheat, so it contains allergens from both — though extensive fermentation breaks down most of the intact allergenic proteins.

For people with histamine sensitivity, soy sauce can be a significant daily source that goes unnoticed because it is used in small amounts in cooking. Coconut aminos (made from fermented coconut sap) is the most practical alternative — it is soy-free, wheat-free, and typically has lower histamine levels.