Histamine intolerance is one of those conditions that can take years to pin down. The symptoms are so varied and so easily mistaken for other things that most people go through rounds of allergy tests, GP visits and dietary experiments before they land on histamine as the issue. Some never get there at all.
I see it regularly in my clinic. Someone comes in with a grab-bag of symptoms that don’t seem related. Bloating after meals, skin flushing, headaches that come out of nowhere, a stuffy nose with no cold. They’ve often been told it’s IBS, or stress, or hayfever. Sometimes all three at once. But when we start mapping their symptoms against what they’re eating, a pattern shows up fairly quickly.
This article covers what histamine intolerance actually is, why it happens, what to eat and what to avoid, and how to work out whether histamine is behind your symptoms
What is Histamine Intolerance?
Histamine is a chemical your body produces naturally. It’s involved in your immune response, it helps regulate stomach acid for digestion, and it works as a neurotransmitter in the brain affecting sleep, appetite and mood. You also take in histamine through certain foods.
Under normal circumstances, your body breaks histamine down as fast as it produces or absorbs it. The main enzyme responsible for this is diamine oxidase (DAO), which sits in the lining of your gut. A second enzyme called HNMT handles histamine breakdown inside your cells.
Histamine intolerance happens when this system falls out of balance. Either you’re taking in or producing more histamine than your body can clear, or your DAO enzyme isn’t working well enough to keep up. The histamine builds up, and once it crosses a certain threshold, symptoms appear.
This is why it’s so confusing for most people. You might eat cheese on Monday and feel fine. Eat the same cheese on Thursday after a week of high-histamine meals and suddenly you’ve got a migraine. It’s not the cheese on its own. It’s the cumulative load.
Histamine Intolerance Symptoms
The symptom list for histamine intolerance is long, which is part of why it gets missed so often. Histamine receptors exist throughout the body, so when levels get too high the effects can show up almost anywhere.
Gut symptoms: bloating, stomach cramps, diarrhoea, nausea, acid reflux. Often diagnosed as IBS.
Skin: flushing (especially after eating or drinking alcohol), hives, itching, eczema flare-ups. Often put down to allergies.
Head and sinuses: headaches, migraines, a blocked or runny nose, sneezing. Often blamed on hayfever or sinusitis.
Nervous system: brain fog, anxiety, difficulty sleeping, dizziness. Often attributed to stress.
Heart and circulation: racing heart or palpitations, drops in blood pressure, feeling lightheaded when standing up.
Hormonal: many women notice symptoms worsen around their period. Oestrogen and histamine influence each other, so hormonal fluctuations can push histamine levels over the threshold.
If you’re looking at that list and thinking “that’s half the things wrong with me,” you’re not alone. The hallmark of histamine intolerance is that the symptoms seem unrelated until you realise they all spike after the same types of food.
What causes it?
Several things can drive histamine intolerance, and in my experience it’s usually a combination rather than a single factor.
Low DAO enzyme activity. This is the most common underlying cause. Your DAO enzyme might be genetically lower than average, or something might be suppressing it. Common DAO blockers include NSAIDs (ibuprofen, aspirin), certain antidepressants, and some blood pressure medications. If your symptoms started or worsened around the time you began a new medication, that’s worth looking at.
Gut damage or inflammation. DAO is produced in the intestinal lining. If that lining is compromised, whether from coeliac disease, inflammatory bowel disease, SIBO (small intestinal bacterial overgrowth), or chronic gut inflammation, DAO production drops. This is why I often see histamine intolerance alongside other digestive conditions. The gut problem came first, and the histamine issues followed.
Gut bacteria imbalance. Certain species of gut bacteria produce histamine as a byproduct. When these strains overgrow, internal histamine production goes up. This is one reason why some probiotics make histamine-intolerant people feel worse. Strains like Lactobacillus casei and Lactobacillus bulgaricus are histamine-producing. Others like Lactobacillus rhamnosus and Bifidobacterium infantis can actually help lower histamine.
High dietary histamine. Some people have borderline DAO function that copes fine with a normal diet but can’t handle a consistently high-histamine one. Aged, fermented and leftover foods are the main culprits.
Nutrient deficiencies. DAO needs specific nutrients to function properly, particularly vitamin B6, vitamin C, copper and zinc. If any of these are low, enzyme activity drops.
High histamine foods to avoid
Histamine content in food increases with age, fermentation, and bacterial activity. As a general rule: the longer something has been stored, processed or fermented, the higher the histamine.
Foods that are high in histamine:
- Aged and hard cheeses (parmesan, cheddar, gouda, blue cheese)
- Cured and smoked meats (salami, chorizo, bacon, ham)
- Tinned or smoked fish (tuna, mackerel, sardines, anchovies)
- Fermented foods (sauerkraut, kimchi, kombucha, miso, soy sauce)
- Alcohol, especially red wine, champagne and beer
- Vinegar and vinegar-based condiments (ketchup, pickles, mustard)
- Leftovers and reheated food (histamine builds as food sits)
- Overripe or dried fruit
Foods that trigger histamine release (even though they’re not high in histamine themselves):
- Tomatoes
- Strawberries
- Citrus fruits (oranges, lemons, grapefruit)
- Spinach and aubergine
- Shellfish
- Chocolate
- Egg whites
One thing that catches people out is leftovers. You might cook a perfectly low-histamine chicken dinner, but if you eat the leftovers two days later, the histamine content will have risen significantly. Batch cooking and freezing immediately is fine. Storing cooked food in the fridge and eating it days later is not.
Low histamine foods you can eat
A low histamine diet doesn’t have to feel restrictive once you know what’s safe. There’s plenty to work with.
Proteins: freshly cooked meat (chicken, turkey, lamb), fresh fish eaten the same day it’s bought or defrosted, eggs (the yolks are fine; some people react to whites)
Vegetables: most vegetables are low histamine. Courgette, broccoli, cauliflower, cucumber, lettuce, sweet potato, carrots, peppers, asparagus, onions, garlic
Fruits: apples, pears, blueberries, cherries, grapes, mango, melon, peaches
Grains: rice, oats, quinoa, millet, buckwheat, most gluten-free grains
Dairy alternatives: oat milk, coconut milk, rice milk (dairy is often tolerated if it’s fresh, but aged cheese is not)
Fats: olive oil, coconut oil, butter (if dairy is tolerated), ghee
Herbs: basil, oregano, thyme, rosemary, coriander, parsley, turmeric, ginger
The key principle is freshness. Buy fresh, cook fresh, eat fresh. Freeze anything you’re not eating straight away rather than leaving it in the fridge.
How to test for histamine intolerance
There’s no single definitive test for histamine intolerance, which is part of why it goes undiagnosed for so long. But there are several approaches that help build the picture.
DAO blood test. Measures the activity level of your DAO enzyme. Low DAO activity alongside symptoms that correlate with high-histamine food is a strong indicator. This test can be arranged privately through a nutritional therapist.
Blood histamine levels. Can show whether circulating histamine is elevated. Useful but not always reliable on its own because levels fluctuate throughout the day.
Food and symptom diary. Honestly, this is often the most revealing tool. Two weeks of writing down what you eat and how you feel afterwards will usually show the pattern more clearly than any blood test. I ask all my clients to do this before we meet.
Elimination diet. A structured low-histamine diet for two to four weeks, followed by controlled reintroduction. If symptoms improve significantly on the elimination phase, that tells you a lot. This is the gold standard approach and the one I use most in practice.
Skin prick test and IgE testing. These rule out true allergies, which is important because the symptoms overlap. If allergy tests come back negative but you’re still reacting to foods, histamine intolerance becomes much more likely.
How to clear histamine from your body
Lowering your histamine load isn’t just about cutting foods out. It’s about supporting your body’s ability to break histamine down properly.
Follow a low histamine diet. This is the foundation. Reduce the incoming histamine so your body can start clearing the backlog. Most people notice a difference within the first one to two weeks. The diet doesn’t need to be permanent. Once symptoms settle and the gut has healed, many people can reintroduce moderate amounts of high-histamine food without problems.
Support your DAO enzyme. The nutrients DAO depends on are vitamin B6, vitamin C, copper and zinc. If any of these are low, the enzyme can’t do its job. A blood test can identify deficiencies. In some cases, a DAO supplement taken before meals can also help.
Fix the gut. If gut inflammation, SIBO or dysbiosis is driving the histamine intolerance, you won’t fully resolve it by diet alone. You need to address the underlying gut issue. This is where working with a practitioner makes a real difference, because the gut work needs to be done in the right order and with the right approach for your specific situation.
Choose the right probiotics. This is a common mistake. People take a generic probiotic and feel worse because it contains histamine-producing strains. Low-histamine probiotic strains include Lactobacillus rhamnosus, Bifidobacterium infantis, Bifidobacterium longum and Lactobacillus plantarum. Avoid products containing Lactobacillus casei, Lactobacillus bulgaricus and Streptococcus thermophilus until your histamine levels are under control.
Manage stress. Stress triggers mast cells to release histamine. If you’re living in a constant state of stress, you’re adding to your histamine load regardless of what you eat. This isn’t about doing yoga once a week. It’s about addressing whatever is keeping your nervous system in overdrive.
Natural antihistamine support. Quercetin is a flavonoid with well-documented mast cell stabilising properties. Vitamin C acts as a natural antihistamine. Stinging nettle has traditionally been used for histamine-related symptoms. These can all be helpful alongside dietary changes, though I’d recommend guidance on dosing rather than guessing.
Histamine intolerance and your gut
I’ve touched on this throughout the article because it’s central to how I approach histamine intolerance in practice. In the majority of cases I see, the gut is involved. Sometimes it’s the primary driver.
DAO is produced in the intestinal lining. If that lining is inflamed or damaged, DAO output drops. Gut bacteria imbalances can independently raise histamine production. And conditions like SIBO create a double problem because they both increase histamine and reduce the enzyme that clears it.
This is why a low histamine diet on its own sometimes helps but doesn’t fully resolve things. The diet manages the symptom. The gut work addresses the cause.
I’ve written about the gut-brain connection in a separate article if you want to understand more about how gut health affects symptoms beyond digestion.
Histamine intolerance vs MCAS
These two conditions get confused because they share a lot of symptoms. But the mechanism is different.
With histamine intolerance, the problem is that your body can’t break down histamine fast enough. The histamine itself is coming from normal sources (food, gut bacteria) but the clearance system isn’t keeping up.
With mast cell activation syndrome (MCAS), the problem is that your mast cells are overreacting and releasing too much histamine (plus other inflammatory mediators) in response to triggers. The breakdown system may be perfectly fine but it’s being overwhelmed by excess production.
The distinction matters because the treatment approach differs. Histamine intolerance often responds well to dietary changes and DAO support. MCAS typically needs additional mast cell stabilising strategies.
In practice, the two can overlap. If dietary changes help but don’t fully resolve your symptoms, MCAS is worth investigating.
I’ve written about MCAS separately if you’d like to understand the differences in more detail.
When to work with a nutritional therapist
You can make a start on a low histamine diet on your own using the food lists above. For some people that’s enough to feel significantly better. But if your symptoms are severe, if they’ve been going on for a long time, or if you suspect a gut issue is driving the problem, working with someone who can test properly and guide the process step by step is worth it.
I help clients identify whether histamine is genuinely the issue (and not something else mimicking it), arrange the right testing, build a workable low-histamine meal plan, address underlying gut problems, and reintroduce foods at the right pace so the diet doesn’t stay restricted forever.
If you’d like to talk it through, I offer a free 30-minute health support call. No obligation, no pressure. Just a conversation about what you’re dealing with and whether I can help.
