By Dr Priya Bhana
Histamine: What It Does to the Body, and Why It Sometimes Goes Wrong
Histamine is a natural chemical your body relies on every day — for digestion, for your sleep-wake cycle, and for your immune response. Symptoms like sneezing and itchy eyes are the most familiar sign of it at work, but when the body makes too much or can’t break it down fast enough, histamine can also show up as bloating, headaches, skin reactions, fatigue, and hormone-related symptoms that are easy to miss or misattribute.
For many of us, Spring is welcomed with open arms — the end of a long winter, more time outdoors, the return of colour. For others, it means never-ending sneezing, coughing, and itchy, watery eyes, and taking an antihistamine daily just to open a window. Why?
What Is Histamine and What Does It Do in the Body?
Histamine is an organic compound found naturally in the body. We also get it from food, and it’s produced by mast cells (a type of white blood cell) as part of our immune reaction. It’s important for several reasons:
- It works as a neurotransmitter, sending messages to the brain.
- It helps digestion by triggering the release of stomach acid.
- It’s released after an allergic reaction or injury as part of the immune response.
The body needs a balance of histamine. When it isn’t broken down properly, or too much is being made, it can build up and lead to what’s known as histamine intolerance.
What Causes High Histamine Levels?
- Bacterial overgrowth in the gut from insufficient stomach acid or poorly digested food — some gut bacteria trigger the body to produce excess histamine.
- Eating histamine-rich foods, such as cheese, wine, and cured meat.
- Insufficient DAO (diamine oxidase), the enzyme responsible for breaking down excess histamine in the gut. Alcohol, green tea, black tea, and some energy drinks are known to block this enzyme. A 2025 review in the International Journal of Biological Macromolecules looked specifically at DAO deficiency and its role in histamine intolerance (Alemany-Fornés et al., 2025).
Research has also shown an association between high gut histamine and “leaky gut” conditions such as IBS and SIBO — something we’ve written about separately if you want to go deeper on intestinal permeability.
Symptoms of High Histamine and Histamine Intolerance
- Bloating, diarrhoea, or stomach cramps
- Headaches, migraines, brain fog, or fatigue — particularly after eating
- Itching, hives, flushing, or swelling (including in the fingers)
- A “globus” sensation (a lump-in-the-throat feeling)
- Nasal congestion or a runny nose unrelated to a cold
- Increased thirst
- Heat intolerance
- In more severe reactions: wheezing, low blood pressure, or a fast heart rate
Histamine intolerance shouldn’t be self-diagnosed, particularly because many of these symptoms overlap with other conditions — but recognising the pattern is often the first step to getting the right support.
Histamine and Sleep, Focus, and Mood
Histamine is part of the sleep-wake cycle — at the right levels, it helps keep the brain alert and motivated, which is why antihistamines (which block this stimulation) tend to make people drowsy. Just like in the gut, an enzyme called HMNT is responsible for breaking down excess histamine in the brain. When there isn’t enough of it, symptoms like headaches, migraines, fatigue, brain fog, and anxiety can follow. Eating the right foods helps HMNT do its job; supplements such as quercetin and butterbur can help too, though it’s worth getting guidance on dose and duration rather than self-prescribing.
Histamine, Skin, and the Immune System
As part of the immune response to injury, pathogens, or allergens, histamine is released from mast cells — found in the gut, lungs, skin, and around blood vessels. This can show up as hives, itching, or swelling after an insect bite, sting, or allergen exposure, and the same inflammatory process happens internally in the gut, heart, and lungs when the body responds to a virus or bacteria — sometimes causing wheezing or breathing difficulty, or changes in blood pressure and heart rate. Mast cells have also been studied for their role in the inflammatory response seen in some respiratory infections, including COVID-19, and some people with long Covid have found antihistamines and mast cell stabilisers helpful as part of their care.
Histamine and Hormones: The Oestrogen Connection
Histamine symptoms are more common in women and often track with the menstrual cycle — flaring when oestrogen is high, around ovulation and just before a period. Oestrogen stimulates mast cells to release histamine and blocks the DAO enzyme that clears it, while histamine in turn stimulates the ovaries to produce more oestrogen — a cycle that research has shown can amplify itself (Jensen et al., 2010). Progesterone, by contrast, stabilises mast cells and supports DAO activity, which tends to reduce histamine.
Many symptoms attributed to “oestrogen dominance” — worse PMS, brain fog, fatigue, cold hands and feet, mood swings, irregular periods, low libido — may actually be histamine or mast cell activity. This is one of the reasons hormone symptoms and histamine intolerance so often get tangled together, and why a full-picture assessment matters.
Managing Histamine Intolerance
- Identifying which foods raise your particular histamine load
- Targeted probiotics and supplements, chosen for your situation
- Understanding your personal histamine threshold, rather than avoiding everything indefinitely
Genetic testing can also show whether you carry variants affecting DAO and HMNT production — something we cover in our nutrigenomics testing service, which looks at how your genes influence how you process histamine, whether that’s histamine from food or histamine that your body is making naturally.
Frequently Asked Questions
What does histamine do to the body? It acts as a neurotransmitter, helps trigger stomach acid for digestion, and is released as part of the immune response to allergens, injury, or infection. In balance, it’s essential; in excess, it can cause wide-ranging symptoms.
What causes histamine to increase? Gut bacterial imbalances, histamine-rich foods (aged cheese, wine, cured meats), and low DAO enzyme activity are the most common contributors.
What are the symptoms of high histamine levels? Bloating, headaches, skin itching or swelling, nasal congestion, thirst, fatigue, and hormone-related symptoms that flare around ovulation or before a period.
Is histamine intolerance the same as a food allergy? No. A true allergy involves the immune system reacting to a specific trigger, often quickly and consistently. Histamine intolerance is usually about the body’s capacity to break histamine down, so reactions can build gradually and vary with overall histamine load.
Histamine intolerance shouldn’t be self-diagnosed. If this sounds familiar, speak to your GP, or book a free discovery call with the Mosaic Medical team to talk through what’s going on.
Dr Priya Bhana is a Functional Medicine GP in South West London.