Histamine Intolerance: Symptoms, Causes and How a Low-Histamine Diet Can Help
I have been seeing more clients recently who suspect that histamine may be playing a role in their symptoms. They often describe headaches, flushing, digestive discomfort, skin reactions, fatigue, or feeling unwell after eating certain foods, but without a clear explanation as to why.
For some people, histamine intolerance may be part of the picture.
This is still an emerging area of research, and there is not yet one single test that gives a simple yes or no answer. But what we do know is that histamine symptoms can happen when the amount of histamine a person is exposed to is greater than their body’s ability to break it down.
In practice, histamine issues rarely come down to just one food or one enzyme. Gut health, hormones, genetics, alcohol, stress, medications, and food storage can all play a role. That is one reason why symptoms can feel so inconsistent and frustrating. histamine?
Histamine is a naturally occurring compound involved in several important processes in the body. It acts as a signalling molecule in the immune system, digestive system and nervous system. It helps regulate immune responses, stomach acid production, gut motility, neurotransmission and blood vessel dilation. Histamine is also present in a range of foods, particularly those that are fermented, aged, processed or stored for longer periods.
Normally, histamine is broken down efficiently. Problems may arise when histamine intake is high, histamine release is increased, histamine degradation is impaired, or several of these occur at the same time.
Histamine intolerance symptoms
Because histamine receptors are found throughout the body, symptoms can affect multiple systems. Reported symptoms commonly include skin, digestive, neurological, cardiovascular and respiratory features.
Skin
Flushing
Itching
Hives
Eczema flare-ups
Digestive system
Bloating
Abdominal pain
Diarrhoea
Nausea
Nervous system
Headaches or migraines
Brain fog
Dizziness
Cardiovascular system
Rapid heartbeat
Low blood pressure
Feeling light-headed
Respiratory system
Nasal congestion
Runny nose
Asthma-like symptoms
Many clients notice symptoms after foods such as wine, leftovers, fermented foods, or aged products. Others find their reactions change from day to day, which can be confusing. A food may seem fine one day, then cause symptoms the next, depending on what else is going on in the body.
Why histamine problems occur
Histamine intolerance is often described as an imbalance between histamine exposure and the body’s capacity to break it down. Two enzymes are particularly important here: DAO and HNMT.
Diamine oxidase (DAO)
DAO is produced mainly in the intestinal lining and helps break down histamine from food before it enters the bloodstream. For this reason, DAO is especially relevant when symptoms are triggered by high-histamine meals, leftovers, alcohol or fermented foods. Reduced DAO activity has been linked with gut inflammation and other gastrointestinal factors, and it is one of the most commonly discussed mechanisms in histamine intolerance.
Histamine-N-methyltransferase (HNMT)
HNMT works mainly inside cells, where it helps inactivate intracellular histamine. It is active in tissues such as the kidneys, liver, airways and nervous system. HNMT is a SAM-dependent methyltransferase, meaning it uses S-adenosyl-methionine (SAM) as a methyl donor.
This matters clinically. Some people seem to react mainly to dietary histamine in the gut, where DAO is especially relevant. Others may have a broader issue with intracellular histamine handling, where HNMT may also matter.
How Your Body Breaks Down Histamine
The body has natural systems that help keep histamine levels within a healthy range.
In a healthy digestive system:
Histamine from food enters the gut.
The enzyme DAO acts as a “histamine filter”, breaking down histamine before it enters circulation.
Histamine is converted into harmless breakdown products.
These by-products are safely cleared from the body.
When DAO activity is reduced, more histamine may enter the bloodstream and contribute to symptoms.
Nutrients that support histamine breakdown
Histamine breakdown depends on several nutrients and pathways in the body.
For the DAO pathway, nutrients such as vitamin B6, copper and vitamin C may be helpful. For the HNMT pathway, the body also needs good methylation support.
This helps explain why histamine issues can look different from one person to another. Some people may need more support for gut health and DAO activity, while others may also benefit from supporting methylation and the body’s ability to clear histamine inside cells.
The role of gut health
Gut health appears to play an important role in histamine balance.
Dysbiosis
Some gut bacteria can produce histamine, while others may help degrade it. When the microbiome becomes imbalanced, histamine-producing bacteria may become more dominant.
Small intestinal bacterial overgrowth (SIBO)
SIBO is increasingly being investigated as a possible contributor to histamine-related symptoms through bacterial fermentation, inflammation and effects on the intestinal environment.
Intestinal inflammation
Because DAO is produced in the intestinal lining, inflammation or damage to the gut lining may reduce histamine tolerance.
Understanding the histamine bucket
A useful way to explain symptoms is the histamine bucket model.
Throughout the day, histamine can accumulate from different sources, including:
Histamine-containing foods
Alcohol
Gut bacteria
Allergic reactions
Infections
Stress
Hormonal fluctuations
Certain medications
If histamine builds up faster than the body can break it down, the bucket may eventually overflow, triggering symptoms. This helps explain why someone may tolerate a food one day but react to it on another when several triggers occur together.
Hormones and histamine
Hormones can also influence histamine symptoms, especially in women.
There seems to be a two-way relationship between histamine and oestrogen, which may help explain why some women notice symptoms getting worse around ovulation or before their period.
This can be particularly relevant in clients who experience migraines, flushing, skin symptoms, or worsening food reactions at certain times in the cycle.
Testing for histamine intolerance
There is currently no single definitive test for histamine intolerance. Diagnosis is usually based on a combination of symptom patterns, clinical history, response to dietary changes and investigation of possible underlying drivers.
Tests sometimes used in practice include:
DAO activity testing
Plasma histamine testing
SIBO breath testing
Stool analysis
Coeliac screening
None of these should be seen as a perfect stand-alone diagnostic answer.
The low-histamine diet
A low-histamine diet aims to reduce the overall histamine load entering the body. In most cases, this is best used as a short-term strategy, while underlying drivers are explored. Recent reviews also warn against unnecessary long-term restriction, as this can increase food fear and nutritional inadequacy.
Foods commonly higher in histamine
Aged cheeses
Fermented foods
Alcohol
Processed or cured meats
Smoked fish
Vinegar-containing foods
Leftovers stored for too long
Histamine levels in foods can vary significantly depending on freshness, storage, ripeness and processing, which is one reason food lists are often inconsistent.
Why leftovers can trigger symptoms
Histamine can increase in food over time as bacteria break down amino acids during storage. This is why some people react more strongly to leftovers, slow-cooked meats, soups, stews and stored fish than to freshly prepared meals. Keeping food cold helps slow histamine formation, and freezing leftovers promptly is usually a better option than keeping them in the fridge for several days. Freezing does not remove histamine that has already formed, but it can help limit further buildup.
For clients following a low-histamine diet, a practical approach is to eat meals freshly cooked where possible, and if saving a portion, cool and freeze it quickly rather than leaving it sitting or storing it in the fridge for long periods. A “within about 2 hours” rule can be a useful food-safety habit, but it should be seen as a practical guideline rather than a proven histamine-specific cutoff.
Nutritional support and supplements
Supplements are best viewed as supportive tools, not a replacement for working on root causes.
Quercetin
Quercetin is a flavonoid found in foods such as red onions, apples, berries, grapes and some brassica vegetables.
Quercetin has attracted attention because of its potential mast cell stabilising and anti-inflammatory effects.
Vitamin C
Vitamin C is often used in histamine support strategies and may support overall histamine handling.
Green tea
Green tea contains polyphenols, including EGCG, which may influence mast cell activity. Some people find it helpful, but evidence that drinking green tea with meals reliably reduces histamine reactions is still limited.
Common mistakes on a low-histamine diet
Some of the most common mistakes include:
Staying on the diet for too long
Focusing only on food and ignoring underlying causes
Relying on rigid or conflicting food lists
Eating too many leftovers
Over-restricting nutrient-dense foods
Overlooking gut health
Assuming all clients need only DAO support
Histamine intolerance vs mast cell activation
Histamine intolerance is sometimes confused with mast cell activation syndrome (MCAS). In histamine intolerance, symptoms are generally discussed in terms of histamine accumulation and reduced breakdown. In MCAS, the issue is excessive or inappropriate release of mediators such as histamine from mast cells. The symptoms can overlap, but MCAS may involve more severe and systemic reactions.
When to seek medical advice
Medical advice should be sought if symptoms include:
Recurrent severe allergic reactions
Breathing difficulties
Fainting episodes
Significant drops in blood pressure
These symptoms require proper medical evaluation and should not be self-managed through diet alone.
Final thoughts
Histamine intolerance can feel confusing and restrictive at first, but it is often more manageable once the underlying patterns become clearer.
In many cases, this is not just about avoiding a few foods forever. It is about understanding the bigger picture: histamine load, gut health, enzyme capacity, hormones, inflammation, medications, and individual susceptibility.
A low-histamine diet can be a helpful short-term tool, but the long-term goal is usually to improve tolerance, expand the diet where possible, and address the reasons why histamine symptoms developed in the first place.
References
Maintz L, Novak N. Histamine and histamine intolerance. Am J Clin Nutr. 2007;85(5):1185–1196.
Schwelberger HG. Histamine intolerance: a metabolic disease? Inflamm Res. 2010;59(Suppl 2):S219–S221.
Comas-Basté O, Sánchez-Pérez S, Veciana-Nogués MT, Latorre-Moratalla ML, Vidal-Carou MC. Histamine Intolerance: The Current State of the Art. Biomolecules. 2020;10(8):1181.
Hrubisko M, Danis R, Huorka M, Wawruch M. Histamine Intolerance—The More We Know the Less We Know. A Review. Nutrients. 2021;13(7):2228.
Kovacova-Hanuskova E, Buday T, Gavliakova S, Plevkova J. Histamine, histamine intoxication and intolerance. Allergol Immunopathol (Madr). 2015;43(5):498–506.
