Histamine intolerance is a condition in which histamine exposure exceeds the body’s ability to break down histamine efficiently. Histamine is a biogenic amine made in the body and also found in varying amounts in foods. It participates in immune signaling, stomach acid regulation, blood vessel tone, skin response, nervous system signaling, and intestinal activity. The main enzyme involved in breaking down ingested histamine in the gut is diamine oxidase, while histamine N-methyltransferase is important in several internal tissues. When histamine formation, intake, release, or impaired degradation becomes greater than clearance capacity, symptoms may appear across several body systems. Common patterns include flushing, itching, hives, nasal congestion, headache, dizziness, palpitations, abdominal cramping, bloating, diarrhea, nausea, menstrual symptoms, fatigue, and brain fog. The symptoms are often variable because histamine receptors exist in many tissues, including the gut, skin, blood vessels, respiratory tract, and nervous system. Histamine intolerance is not the same as a classic food allergy. It is commonly described as a pseudoallergic or intolerance pattern involving excess histamine load, reduced degradation capacity, intestinal barrier stress, microbiome imbalance, mast-cell signaling, and inflammatory regulation. The digestive tract is central because food histamine is normally degraded in the intestinal lining before it enters circulation. Reduced diamine oxidase activity, gut inflammation, epithelial irritation, alcohol exposure, processed foods, food additives, and microbial imbalance may increase histamine burden or reduce tolerance. Some foods naturally contain more histamine or may accumulate histamine through aging, fermentation, storage, or microbial activity. A whole-food plant-based approach for histamine intolerance emphasizes fresh, minimally processed plant foods selected for lower histamine burden, antioxidant capacity, epithelial barrier support, and microbiome balance. A Plant-Based Diet emphasizes fresh cooked brown rice, quinoa, millet, sweet potato, carrots, broccoli, kale, cucumber, romaine lettuce, blueberries, apples, pears, pumpkin seeds, chia seeds, flax seeds, ginger, turmeric, parsley, and green tea. These foods provide vitamin C, vitamin B6, folate, magnesium, potassium, manganese, zinc, copper, fiber, polyphenols, flavonoids, carotenoids, and glucosinolate-related compounds. Their biological relevance centers on gut barrier integrity, oxidative stress regulation, immune response signaling, mast-cell-associated inflammatory balance, short-chain fatty acid signaling, and glutathione defense. The goal is to reduce histamine burden while supporting nutrient sufficiency, microbial diversity, epithelial resilience, and balanced immune signaling through whole plant foods.