What is Histamine Intolerance, DAO Deficiency and MCAS?

This information is for general educational and informational purposes only and is not intended to substitute for professional medical advice, diagnosis, or treatment. If you believe you may be experiencing any of the conditions described below, please consult a qualified healthcare provider.

What is Histamine?

Before understanding histamine intolerance, DAO deficiency, and MCAS, it helps to understand what histamine actually is. Histamine is a naturally occurring compound found in the human body and in many foods and beverages. In the body, it plays important roles in immune response, digestion, and neurological function. It is also present in elevated amounts in fermented, aged, and cured foods — including red wine, aged cheeses, cured meats, and fermented vegetables such as kimchi — and alcoholic beverages can both contain histamine and affect the body's natural ability to clear it.*

The body has two primary enzymes responsible for managing histamine levels: Diamine Oxidase (DAO), which works primarily in the digestive tract to break down histamine from food and drink, and Histamine N-Methyltransferase (HNMT), which manages histamine inside cells. When these systems are working well, histamine levels are naturally regulated. When they are not, histamine may accumulate — and that is where these three distinct concepts come in.*

Histamine Intolerance (HIT): A Clearance Problem

Histamine intolerance — sometimes referred to as histamine sensitivity — is generally understood in the research literature as a mismatch between the amount of histamine entering or being produced in the body and the body's capacity to break it down.* Histamine intolerance is not a true allergy, but a condition where the body has difficulty breaking down histamine from foods. This can happen when there is a deficiency or lack of activity in the enzyme Diamine Oxidase (DAO), which is responsible for degrading histamine in the gut. When DAO is not working properly, histamine levels can build up, leading to responses that often mimic an allergic reaction. 

For some people, the histamine load fills primarily from food-derived sources due to low DAO activity, leading to what is described as histamine intolerance. It is dose-dependent — meaning that smaller amounts of histamine may be tolerated while larger amounts may provoke a response — and it is typically linked to what is consumed.* 

Common areas where histamine sensitivity may be experienced include the digestive tract, skin, sinuses, cardiovascular system, and neurological function.* These experiences are variable, may seem unrelated to one another, and can easily be mistaken for other conditions.*

This content is educational in purpose only and does not constitute a diagnosis. Always consult a healthcare provider to discuss your individual health history.

DAO Deficiency: The Enzyme at the Center of Histamine Intolerance

The body naturally produces the DAO enzyme, but various factors can lead to a deficiency or reduced activity, including genetics, certain medications, alcohol consumption, and imbalances in gut health. 

DAO is the primary enzyme for degrading extracellular histamine and is predominantly responsible for breaking down histamine in the digestive tract. When DAO is insufficient, histamine from dietary sources — including aged foods, fermented products, and certain fruits and vegetables — may accumulate in the body.* DAO deficiency is therefore understood as a contributing factor to histamine sensitivity, not a separate disease.* 

Serum DAO activity testing is available but has limited reliability, and a normal result does not necessarily rule out histamine sensitivity. If you suspect DAO deficiency may be relevant to your experience, consult a qualified healthcare professional who can assess your individual situation.

Supporting the body's natural DAO enzyme activity through dietary supplementation is one approach some individuals explore in consultation with their healthcare providers.* OmneDiem® Histamine Digest® supplies Diamine Oxidase (DAO) to support the body's natural histamine breakdown process in the gut.* It is not intended to diagnose, treat, cure, or prevent any disease or health condition.

MCAS (Mast Cell Activation Syndrome): A Different Mechanism

Mast Cell Activation Syndrome (MCAS) is a distinct condition from histamine intolerance, though the two share overlapping characteristics and are frequently confused. Understanding the difference is important — and requires working with a qualified medical provider for proper evaluation.*

Histamine intolerance is driven primarily by histamine. In contrast, MCAS involves histamine as well as other mediators including tryptase, leukotrienes, and prostaglandins. Histamine intolerance is usually linked to a deficiency in the DAO enzyme or impaired HNMT activity. MCAS stems from dysregulated mast cell activity, leading to the release of multiple inflammatory mediators.*

Mast cells are tissue-resident immune cells that live in the skin, gut, lungs, sinuses, and around blood vessels and nerves. They normally release inflammatory mediators in response to genuine threats. In MCAS, they may become hyperreactive and release these mediators in response to triggers that would not normally provoke a reaction.* 

Histamine intolerance is generally assessed based on symptom history, DAO measurement, or an elimination diet. MCAS assessment is more complex and may involve mediator panels and additional clinical evaluation.* MCAS is a medical condition that requires diagnosis and management by a qualified healthcare provider. It is beyond the scope of dietary supplements to treat, cure, or prevent MCAS or any other disease.* 

Those who have MCAS tend to have sensitivities beyond just histamine-containing foods. If mast cells are not broadly overreactive, some individuals find that supporting histamine breakdown through supplements like DAO may be part of their overall approach — always in consultation with a practitioner.* 

How OmneDiem® Histamine Digest Supplements May Support Those Exploring DAO Deficiency or Histamine Intolerance

OmneDiem® specializes in DAO enzyme dietary supplements formulated to support the body's natural histamine management process in the gut.* All OmneDiem® Histamine Digest® products use DAOgest® — a naturally derived, porcine-sourced DAO enzyme — delivered in a designed-release capsule that activates in the small intestine where dietary histamine is processed.*

OmneDiem® Histamine Digest® — 30,000 HDU of DAO per capsule. The foundational formulation for everyday pre-meal support.* Available in 30, 60, and 120 capsule sizes.

OmneDiem® Histamine Digest® PureMAX —  40,000 HDU of pure DAOgest® DAO. OmneDiem's highest-potency, cleanest formulation for those who may benefit from greater DAO support.*

OmneDiem® Histamine Complete — 15,000 HDU of DAO combined with additional ingredients to support healthy seasonal respiratory and sinus function alongside dietary histamine management.* Formulated for broader daily histamine support.*

Always consult your healthcare provider before beginning any new supplement regimen.

* These statements have not been evaluated by the Food and Drug Administration. OmneDiem® dietary supplements are not intended to diagnose, treat, cure, or prevent any disease or health condition, including histamine intolerance, DAO deficiency, or Mast Cell Activation Syndrome. The information provided in this FAQ is for general educational and informational purposes only, does not constitute medical advice, and should not be used as a substitute for consultation with a qualified healthcare professional. References to third-party educational sources are provided for informational context only and do not imply endorsement. Individual results may vary. If you experience symptoms that concern you, consult a qualified healthcare provider. Not for use during pregnancy or breastfeeding without prior consultation with your healthcare provider. OmneDiem® Histamine Digest® products contain a porcine-derived ingredient and are not suitable for individuals with pork allergies or those following vegetarian, vegan, kosher, or halal diets. Keep out of reach of children.