Hist Diamine is a patented enzyme formula containing diamine oxidase (DAO)—the main enzyme responsible for the degradation of ingested histamine. This enzyme has been clinically tested and found to break down food-derived histamine in the digestive tract. Endogenous and exogenous histamine must be broken down in order to maintain homeostasis and histamine balance. The enzyme diamine oxidase (DAO) degrades histamine by converting it from 2-(4-imidazolyl)-ethylamine to the inactive metabolite imidazole acetaldehyde. The active ingredient in Hist Diamine is porcine-derived diamine oxidase, and research suggests that DAO derived from porcine appears to have identical action to DAO. In humans and other mammals, DAO is found in high concentrations in the gastrointestinal mucosa. Animal studies suggest that circulating DAO may be a marker for mucosal integrity and maturity. Histamine tolerance may not be the same for everyone. Results of a double-blind, placebo-controlled crossover study suggest that tolerance to histamine can vary from individual to individual. Total body histamine load must be considered when evaluating histamine tolerance, and a balance between histamine and DAO appears to be crucial to maintaining skin, rhinoconjunctival, and gastrointestinal health. Genetic and environmental factors may interact to influence DAO expression. Ongoing research addresses the role that genetic variations may play in individual differences in DAO metabolism, and serum activity was significantly associated with seven single nucleotide variations within the DAO gene. Histamine tolerance may be reflected in detailed questionnaires, food intake logs, trial with low-histamine diet, and measurement of DAO and histamine. Hist Diamine does not manage or address antibody-related or IgE-related food allergies.