Histamine is a biogenic amine and a chemical compound crucial in various physiological processes within your dog’s body. It is synthesized and stored in certain types of cells, including mast cells and basophils, which are part of the immune system.

A dog produces histamine through the synthesis of the essential amino acid histidine. Histamine is mainly stored in the mast cells and basophils, which are found in almost all tissues in the body. Histamine is released when the body is challenged with a stressor, such as an allergen or a traumatic injury. Histamine causes the blood vessels to expand (vasodilation), allowing an array of immunity cells, including the mast cells and basophils, to flow into the bloodstream and travel to the attack site. 

Histamine is crucial in many functions throughout the body, including:

Inflammation: Histamine is a crucial mediator of the inflammatory response. It causes blood vessels to dilate and become more permeable, which allows immune cells to reach sites of infection or injury more quickly. This leads to redness, swelling, and heat at the site.

Allergic Reactions: In allergic reactions, histamine is released when the immune system identifies an allergen. It triggers clinical signs like itching, sneezing, runny nose, watery eyes, and skin rashes.

Stomach Acid Regulation: In the stomach, histamine stimulates the secretion of stomach acid, which aids food digestion.

Neurotransmission: In the central nervous system, histamine acts as a neurotransmitter, helping to regulate sleep-wake cycles, appetite, and mood.

Immune Response: Histamine is involved in immune responses, including activating specific immune cells and enhancing other immune processes.

Blood Pressure Regulation: Histamine can cause blood vessels to dilate, which can affect blood pressure regulation.

Histamine functions are usually well-regulated by the body's systems. However, in some cases, excessive histamine release can lead to health issues, such as allergic reactions, histamine intolerance, or conditions like mast cell tumors in dogs.

Once histamine has performed its function, the body removes it via enzymatic inactivation pathways. When disrupted, two pathways will cause an overload of histamine. Histamine overload, also known as histamine intolerance or histamine sensitivity, is a condition in which the body cannot properly break down and metabolize histamine, accumulating histamine in the body.

The diamine oxidase (DAO) pathway inhibits DAO, resulting in histamine excesses, and causes gastrointestinal, cardiovascular, respiratory, and skin disorders. The disruption of the histamine-N-methyltransferase (HNMT) pathway affects the nervous system.

The body can become overloaded with histamines during stress, such as physical trauma, infection, nutrient deficiencies (especially B12 or magnesium), inflammation, or excessive exercise. The overload results from the disruption of the inactivation pathways of histamine. 

Common clinical signs of histamine overload or intolerance include:

Skin issues: Itching, hives, rashes, or redness.

Gastrointestinal signs: Abdominal pain, gastric ulcers, bloating, diarrhea, or nausea.

Respiratory signs: Sneezing, runny nose, congestion, or difficulty breathing.

Cardiovascular disease: Fluctuations in blood pressure, rapid or irregular heart rate.

Central nervous system disorders: Anxiety or nervousness or sleep disturbances.

During these episodes, the most common treatment is a histamine antagonist, more commonly known as an antihistamine. However, there are other ways to prevent excess histamine in the body.

Histamine is also found in certain foods and can cause signs in histamine-intolerant individuals. Foods high in histamine include aged cheeses, fermented foods, alcohol, and processed meats. In dogs, histamine release can contribute to clinical signs like itching, redness, and swelling, particularly in allergies or hypersensitivity reactions.

Some foods are high in histamine, and it is theorized that other foods called histamine liberators can cause histamine release by the body's cells. In general, fermented foods have the highest level of histamine. Fresh, unprocessed foods have the lowest levels.

The histamine contents of food vary significantly: for example, freshly caught fish contain almost no histamine, while cured, pickled, or not-so-fresh fish can contain more than 2,000 mg/kg of histamine. Cheese is another food that has significant variation in the concentration of histamine. In general, foods to avoid when wanting to restrict the consumption of histamine are:

Fermented dairy products- cheese (especially aged), yogurt, sour cream, buttermilk, and kefir

Fermented vegetables-sauerkraut and kimchi

Cured or fermented meats- sausages, salami, and ham

Frozen, salted, or canned fish-salmon, sardines, and tuna

Food cooked for extended periods, such as bone broth 

Dietary Supplements that can Diminish the Effects of the Histamine Response

Quercetin is a flavonoid that reduces the release of histamine when your dog is exposed to allergens.

Nettle is used as a tea or tincture that blocks the activity of histamine.

Bromelain is an enzyme found in pineapples and is often supplemented with quercetin for antihistamine effects.

Vitamin C supports the detoxification of histamine.

Vitamin B6, folate, and B12 all support the detoxification of histamine processes.

Despite the body’s need for histamine for more than 14 known functions, an excess can have significant consequences.  

Reducing your dog’s dietary intake is one way to lessen the chance of histamine overload.  

You can also reduce the inhibition of the detoxification pathways by reducing your dog’s environmental exposure to heavy metals, air pollution, pesticides, and weed control chemicals commonly used on lawns.

Histamine: metabolism, physiology, and pathophysiology with applications in veterinary medicine  

Current Trends in Detection of Histamine in Food and Beverages 

The Missing Link: A Case of Severe Adverse Reaction to Histamine in Food and Beverages 

Minimize your Dog’s Histamine Intake by Providing Low-Histamine Foods

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