Histamine is found naturally in the tissues of the body and is released from mast cells as part of an allergic reaction. It stimulates gastric secretion and causes dilation of capillaries, constriction of bronchial smooth muscle, and decreased blood pressure. It plays a role in the movement of white blood cells. Non-mast cell histamine is found in several tissues, including the brain, where it functions as a neurotransmitter. Histamine produces larger pores in the blood vessel walls as the first step in launching an inflammatory response, causing the typical ‘itching, sneezing, wheezing, swelling’ allergy symptoms.

We all have a myriad of microbes living in our guts.  Harmful intestinal bacteria and yeasts contain an enzyme, histidine decarboxylase (HDC), which produces histamine. When there is bacterial overgrowth, such as SIBO (small intestinal bacterial overgrowth) or yeast overgrowth, these microbes can contribute to an increase of histamine. In addition, when tissues are injured by gut dysbiosis and mycotoxins, the damaged cells release yet more histamine. This double source of histamine builds up to toxic levels and causes blood vessels to leak fluid into the tissues, producing inflammation.

Histamine-producing factories

Histamine also occurs naturally in certain foods. We all have an enzyme, Diamine oxidase, which breaks down any histamine that we absorb from these foods, so that the histamine doesn’t affect us. However, high levels of histamine in the gut can overwhelm this enzyme. In addition, gut dysbiosis damages the the gut wall, impairing the ability to produce the enzyme, Diamine oxidase. So people with damaged gastrointestinal systems are at higher risk for histamine intolerance. When they eat histamine-rich foods, they can suffer ‘allergy-like’ symptoms such as headaches, rashes, itching, diarrhoea and vomiting or abdominal pain.

Many people who suffer from histamine intolerance have an excess of bacteria and yeasts that have become histamine-producing factories in the gut. The combination of excess histamine and  deficiencies in the Diamine oxidase enzyme, causes histamine levels to build up to even greater levels. Thus the underlying cause of histamine intolerance is invariably gut dysbiosis. So there needs to be a concerted and  ongoing effort to rebalance the intestinal microflora and heal the gut.

Histamine Reaction

Within minutes a person exposed to histamine may experience:

  • Flushing of face
  • Nausea
  • Headache
  • Runny nose or congestion
  • Dizziness
  • Racing heart
  • Anxiety

If the reaction continues, the following symptoms may occur:

  • Hives
  • Generalized swelling
  • Abdominal cramps 
  • Diarrhea

In severe cases, there may be:

  • Panic attacks
  • Blurred vision
  • Bronchoconstriction, asthma or difficulty breathing
  • Laryngeal edema or swelling of tongue

Here are some additional common reactions:

  • tachycardia, palpitations, light headedness,
  • low blood pressure and fainting
  • constipation and bloating
  • muscle pain, cramps
  • joint pain, arthritis
  • hearing problems, tinnitus
  • attention and memory problems
  • depression, mind racing
  • insomnia, fatigue
  • unexplained bruising and bleeding
  • restless leg syndrome
  • flushing and rosacea


It has been shown that histaminergic cells have the most “wakeful” firing pattern of any neuronal type. They fire rapidly during waking, and completely stop firing during sleep. The cell bodies of neurons which release histamine as a neurotransmitter are found in the posterior hypothalamus. From here, these histaminergic neurons project throughout the brain, to the cortex. Therefore, excessive histamine production causes ‘racing brain’ and insomnia.


Histamine is an important protein involved in many allergic reactions. An antigen must first be attached to cell surface receptors on mast cells. This triggers a response that often includes the release of histamine. Most allergies involve the release of histamine and other pro-inflammatory substances.

Allergic reactions have an adrenal component

Cortisol, one of the primary hormones produced by the adrenal glands, is a strong anti-inflammatory agent. For this reason proper adrenal function plays an important role in mediating the histamine release and inflammatory reactions that produce the symptoms experienced with allergies.

A vicious circle occurs with adrenal fatigue and the tendency to experience allergiesThe more histamine that is released the harder the adrenals have to work to produce more cortisol, thereby the more fatigued the adrenals become, which increases allergic inflammation – a vicious circle.

Stress, histamine and adrenalin

Increased histamine is released during extreme stress. The strongest antihistamine we have is adrenaline that is released by our adrenal glands. This is how stress can exhaust the adrenal glands. Histamine release is probably most significant during periods of panic attack, causing a closing of the airways in the lungs. When released in the lungs, histamine causes the airways to swell shut in an attempt to ‘close the door’ on offending allergens and keep them out. Panic attacks are known for the sense of weight or contraction on the lungs. As a consequence there is a sense of suffocation and lack of oxygen.


Histamine intolerance can cause or exacerbate anxiety and emotional stress.  Emotional stress itself, such as job loss, loss of a loved one, or a chronic relationship conflict – or other lifestyle stress, such as  lack of sleep, or job and family demands can inhibit the body’s ability to produce enzymes.  Or the body is put into stress because normal levels of enzymes are being used up and not sufficiently replaced.

Such stress can impair the production of the enzyme Amylase, which is  involved in anti-inflammatory reactions such as those caused by the release of histamine. It is a natural histamine blocker, which stabilizes mast cells and basophils that release histamine at the start of an inflammatory response.

Excessive carbohydrate consumption

Amylase is also needed to break down starch into sugar. The enzyme is found in human saliva. When we eat carbohydrates, a small amount of digestion takes place as we chew through the actions of the enzyme amylase. However in the stomach, food is bathed in hydrochloric acid, which inhibits starch digestion until food exits the stomach and enters the small intestine (which is why it’s so important to chew food well). Amylase converts starch to glucose which is burned to produce energy for the body. So a deficiency in Amylase can be a major factor in chronic fatigue.

However, the excessive consumption of refined carbohydrates will chronically deplete amylase thereby increasing histamine-related health problems. Chronic carbohydrate consumption causes intestinal toxaemia and creates stress, which exhausts the adrenal glands and the immune system.

Enzymes normally break down allergens into smaller components in order to eliminate it without stressing the body. But in the case of allergic symptoms, when there are inadequate enzymes reserves in the body, histamine is released rather than enzymatic breakdown of the allergens.

Insulin resistance and glucose intolerance

Reduction in amylase levels is associated with insulin resistance and glucose intolerance. Insulin plays a major role in the control of pancreatic amylase biosynthesis. The development of severe insulin resistance (hyperinsulinaemia) is associated with impairment of amylase-gene expression and reduction in glucose metabolism

Pancreatic enzymes are released in response to histamine, as a protective measure against ingestion of allergens and pathogens. If the release of histamine is prolonged, this could lead to the overworking and depletion of the pancreas. This would include a reduction in digestive enzymes and assimilation, coupled with vulnerability of the GI Tract to allergens and pathogens. 

Mitochondrial poison

Inflammation produces nitric oxide.  Nitric oxide is an essential component the body uses in many functions including neurotransmission and vasodilation. However in excess it is also a potent nitrogen free radical with the capacity to kill neurons and cells in generalNitric oxide is a mitochondrial poison. It poisons the mitochondria by blocking the cis-aconitase enzyme and the conversion of citric acid to cis-aconitinic acid, thereby causing chronic fatigue.

Histamine is intimately involved with Nitric Oxide. Histamine up-regulates the generation of nitric oxide, and nitric oxide serves a protective role in down-regulating histamine release from mast cells.  So nitric oxide can act as an anti-inflammatory under normal conditions. However, when over-produced it can lead to inflammation, which in turn releases yet more histamine – which then up-regulates nitric oxide – a vicious circle.

Poor iron status

Several factors increase levels of nitric oxide in the body: Allergies (histamine), poor iron status, hypoxia (oxygen deficiency). Histamine release stimulates nitric oxide synthesis and release. The increased permeability of the blood/brain barrier associated with histamine release is actually mediated by nitric oxide. Low iron levels can increase nitric oxide levels because haemoglobin is one of the complexing factors that bind nitric oxide in the blood rendering it inactiveThus we must assure that our diet contains adequate iron.


Chronic inflammation

Histamine triggers inflammation with far reaching consequences
when it becomes chronic and systemic.