When the body accumulates too much histamine as a result of either an excessive intake or an inability to properly break it down, it can lead to histamine intolerance. Histamine is a chemical that plays a role in digestion, immune responses and nervous system regulation. In the gut, the enzyme diamine oxidase (DAO) normally aids in the breakdown of histamine. However, histamine accumulates and can result in a variety of symptoms, including bloating and water retention, if DAO levels are low or excessive.  

What is Histamine, and What Does It Do in the Body?

The body naturally produces histamine, a chemical that is essential for digestion, the immune system and the central nervous system. It is most well known for its function in allergic reactions, where immune cells known as mast cells and basophils release their reaction to allergens. Itching, swelling, and a runny nose are common allergy symptoms. Histamine helps with digestion by promoting the release of gastric acid, which controls the production of stomach acid. It functions as a neurotransmitter in the brain, affecting alertness and sleep-wake cycles. Histamine is necessary for many body processes; an excess of it or sensitivity to it can result in problems like allergies, asthma or histamine intolerance.

What is histamine intolerance?

A condition known as histamine intolerance occurs when the body cannot properly break down histamine, which causes the body to accumulate histamine and cause symptoms that resemble an allergic reaction. Histamine in food is normally broken down by the enzyme diamine oxidase (DAO), but histamine builds up when DAO levels are low or its function is affected. Many symptoms, such as headaches, flushing, nasal congestion, digestive problems, low blood pressure and irregular heartbeat, can result from this. 

Common symptoms of histamine intolerance?

Common symptoms of histamine intolerance are

• Bloating
• Diarrhoea 
• Nausea
• Runny nose
• Sneezing
• Rapid heart rate 
• Low blood pressure 
• Fatigue 
• Dizziness
• Headaches
• Itchy skin or rashes. 

The Role of Histamine in the Body

Histamine is not bad; it helps regulate stomach acid, dilates blood vessels, contracts smooth muscles and plays a crucial role in allergic reactions. But too much histamine can be harmful. When it attaches itself to receptors throughout the body, especially the H1 and H2 receptors, it can transform vascular permeability, induce inflammation and cause digestive issues. 

How Histamine Triggers Water Retention

One of histamine’s primary functions is to make blood vessels more permeable. In an acute allergic reaction, this helps immune cells get to the tissues that are impacted. The hands, face, abdomen and ankles are among the areas that may experience swelling and water retention as a result of fluids entering the surrounding tissues when histamine levels remain elevated due to intolerance.

Bloating and Gut Inflammation

Bloating and other gut-related symptoms can also result from histamine intolerance. Excess histamine damages the stomach acid balance and causes inflammation by irritating the lining of the digestive tract. Abdominal distension, poor digestion and gas accumulation can result from this irritation. Histamine-rich foods like fermented foods, alcohol and aged cheese may worsen symptoms, causing frequent post-meal bloating. 

Gut-Brain Axis and Fluid Regulation

Histamine also affects the gut-brain axis, which affects the communication between the digestive and neurological systems. Aldosterone, vasopressin, and other hormones involved in fluid balance may be affected by this interaction, which may also result in changes in intestinal motility. Fluid retention and a swollen or bloated feeling can also be caused by disruptions in these hormonal pathways. 

Foods high in histamine

Foods high in histamine are

• Aged cheese
• Cured meats
• Fermented foods
• Smoked or canned fish
• Vinegar-containing foods
• Dried foods
• Tomatoes, spinach, eggplant, avocado

The role of DAO in histamine breakdown

The main enzyme in the digestive system that breaks down histamine is called diamine oxidase (DAO). Histamine can build up in the body when DAO levels are low or its activity is inhibited by genetic factors, certain medications, or inflammation in the gut. Symptoms like headaches, skin reactions, digestive discomfort and respiratory problems could result from this accumulation, and one of the main causes of histamine intolerance is thought to be inadequate DAO activity. 

How stress and hormones affect histamine levels

Histamine levels in the body can be greatly impacted by stress and hormonal changes. The release of certain chemicals, such as cortisol, in response to chronic stress can impair gut function and lower the activity of DAO, the enzyme responsible for breaking down histamine. This may lead to increased histamine buildup and related symptoms. 

Histamine levels can also be influenced by hormones, particularly oestrogen. The symptoms of histamine intolerance can be worsened by high oestrogen levels, which can stimulate histamine release and reduce DAO activity, such as during ovulation or pregnancy. This is why some people, particularly women, may notice histamine-related issues fluctuate with their menstrual cycle or hormonal shifts. 

Managing Histamine Intolerance

Managing histamine intolerance often includes a low-histamine diet, supporting DAO enzyme activity, and addressing underlying gut health. Taking probiotics that don’t release histamine (e.g., Lactobacillus rhamnosus vs. Lactobacillus casei), avoiding histamine-releasing foods, and reducing stress can help stabilise symptoms. In some cases, DAO supplements may help break down histamine more effectively before it triggers symptoms like water retention and bloating.

While often overlooked, histamine intolerance can be a hidden cause behind persistent bloating and water retention. Understanding how histamine affects the vascular and digestive systems gives insight into how even healthy-looking meals can leave some people feeling puffy and uncomfortable. With the right dietary changes and gut support, many people find significant relief from these frustrating symptoms.


Felciya, is a Specialist Dietitian at The London Obesity & Endocrine Clinic. She has helped many patients overcome weight management barriers. ©Simplyweight


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