Histamine intolerance (HIT) is a trending buzzword within the realm of functional nutrition and integrative health. Although mainstream medicine has not officially accepted it as a clinical diagnosis, more and more holistic nutritionists, wellness experts, and alternative practitioners are spreading the word about this condition. They're highlighting a distinctive and intriguing trend: people getting allergy-like symptoms following the intake of specific foods — without being positive for conventional food allergies.So, what is histamine intolerance? Is it the cause of your enigmatic bloating, headaches, skin rashes, or maybe even brain fog? And how do you react to such symptoms?This in-depth guide will break down what is histamine intolerance, the symptoms to look out for, potential causes, and how a low-histamine diet can alleviate your symptoms.What is Histamine?Before going into the condition itself, a basic understanding of histamine's role in the body is important. Histamine is a chemical messenger — or signaling molecule — that plays an important role in a number of physiological processes. Notably, it's implicated in the immune response of the body, digestion, and brain-cell communication.During allergic reactions, the body releases histamine to defend against perceived threats like pollen, dust, or certain foods. This triggers inflammation, causing symptoms like sneezing, congestion, hives, or swelling. But histamine is also found naturally in many foods and is produced daily in the body in small amounts. It’s perfectly normal — until your body can’t break it down efficiently.What Is Histamine Intolerance?Histamine intolerance results when the body fails to metabolize or degrade histamine efficiently — either through enzyme deficiency, gene defects, or dietary load of histamine. This leads to an accumulation of histamine in the blood that triggers symptoms similar to allergic reactions.Contrary to food allergies, where the immune system is involved, histamine intolerance is considered to be more of a metabolic dysregulation. The body has an enzyme called diamine oxidase (DAO), which is released in the small intestine and is used to degrade dietary histamine. When DAO is low or not working optimally, food histamine can build up and initiate a chain of symptoms.Notably, histamine intolerance is not yet officially a recognized medical condition by organizations like the American Academy of Allergy, Asthma, and Immunology. Anecdotal evidence, increasing social media discussions, and early research have propelled it into public health discourse.What Does Histamine Intolerance Feel Like?Histamine intolerance is commonly referred to as the "great mimicker" due to its symptoms, which mimic various other conditions — ranging from allergies to irritable bowel syndrome (IBS) to hormonal disturbances.Typical symptoms are:Gastrointestinal discomfort: bloating, diarrhea, nausea, or cramping in the abdomenSkin symptoms: hives, flushing, itching, and edemaRespiratory symptoms: nasal congestion, wheezing, sneezing, or shortness of breathCardiovascular signs: low blood pressure, dizziness, rapid heart rate or palpitationsNeurological symptoms: headaches, migraines, anxiety, or brain fogSince these symptoms can be so widespread, involving more than one system within the body, they're so frequently misdiagnosed and missed. Someone may see specialist after specialist without getting an explanation, particularly if standard allergy tests yield a negative result.Why Does Histamine Intolerance Occur?There are a couple of main reasons why an individual might develop histamine intolerance:1. DAO Enzyme DeficiencyThe most common cause that has been extensively talked about is a deficiency or malfunction of DAO. If your digestive system is not secreting enough of this enzyme — or if it's inhibited by some foods, drugs, or medical conditions — histamine clearance decelerates, causing accumulation.2. Genetic FactorsOthers can inherit mutations that lead to reduced DAO production or reduced efficiency of the enzyme. Until now, there is limited research, but familial patterns indicate that genetics may be a contributing factor.3. Drugs That Inhibit DAOSome medications, including blood pressure drugs, antidepressants, and antibiotics, can inhibit DAO action or cause histamine accumulation in the body. Opioids and narcotics also might contribute to a histamine accumulation.4. Gastrointestinal DisordersIndividuals with inflammatory bowel conditions such as Crohn's disease or ulcerative colitis tend to exhibit decreased DAO activity as a result of intestinal inflammation. Gut dysbiosis — an imbalance in gut flora — can further inhibit histamine degradation.High-Histamine Foods: What to AvoidAll foods have some amount of histamine, but some are much higher in histamine content — particularly fermented, aged, and processed foods. The longer the food is stored or aged, the greater the histamine content.Foods high in histamine are:Alcohol, especially wine and beerAged cheeses (Parmesan, Gouda)Smoked or cured meats (bacon, salami, ham)Sauerkraut and pickled vegetablesCanned fish (tuna, mackerel)Tomatoes, spinach, eggplantVinegar and soy sauceThere are some other foods that do not have high histamine content themselves but can cause the release of histamine or inhibit DAO activity. They are:Citrus fruitsChocolate and cocoaEgg whitesPeanutsBlack and green teaEnergy drinksCan a Low-Histamine Diet Provide Relief?It's impossible and not necessary to eradicate histamine entirely from your diet. The intention of a low-histamine diet is to lower the total histamine load on your body — taking a break for your digestive system and enzymes.A low-histamine diet typically starts with an elimination period, in which high-histamine foods are eliminated for a period of several weeks. Foods are then gradually reintroduced to determine the culprits. Consulting with a dietitian or nutritionist is highly recommended, particularly to avoid malnourishment.Some examples of low-histamine foods are:Unprocessed, fresh meats and fish (especially those frozen upon catch)Gluten-free grains including rice, quinoa, and milletMost fruits that are not citrus (apples, blueberries, pomegranates, mangoes)Fresh veggies (apart from tomatoes, spinach, eggplant)Coconut and olive oilNon-dairy milk (hemp, almond, coconut)Non-aged cheese such as mozzarella, cream cheese, or ricotta (if dairy is well-tolerated)Important principle: The newer, the better. Freshly prepared foods with no preservatives and minimal storage time are best for the control of histamine levels.Histamine intolerance occupies a gray area in modern medicine. While it lacks formal recognition from most medical authorities, many individuals have found symptom relief through low-histamine diets and targeted lifestyle changes.Research continues to develop, and additional studies must be conducted in order to determine the mechanisms, diagnostic measures, and optimal treatment regimens for HIT. Until then, if you suspect intolerance to histamine, monitor your symptoms, see a healthcare professional, and consider collaborating with a dietician who is knowledgeable about histamine metabolism.