Histamine is largely known for causing allergic reactions. However, it is needed for many processes in the body including the contraction of smooth muscle cells, dilation of blood vessels, lowering blood pressure, it aids in the production of gastric juices to help breakdown food, and it serves as a neurotransmitter among many other things. It's all about having the right amount of histamine.  Too much or too little can lead to adverse symptoms.  Genetic variants can affect whether you make it efficiently or cannot break it down efficiently.
The body uses the DAO and HMNT enzymes to break-down and clear out histamines (DAO is produced by the villi that line the small intestines). The gene that codes for DAO enzyme production is AOC1 which can increase or decrease the production of DAO enzyme. HNMT is the enzyme that regulates histamine via converting it into N-Methylhistamine which is a form that can be eliminated from the body. Looking at methylation pathways can also help balance histamine by creating the methyl group needed for the HNMT enzyme to work.
Genetic variants in the HDC gene can lead to low levels of histamine.  Histamine is used in the production of hydrochloric acid and is considered a neurotransmitter that increases wakefulness. Low levels of histamine lead to fatigue, brain fog and has been linked to Tourett's syndrome. 
When histamine pathways are blocked it can create a build-up of histamine leading to histamine intolerance. Our genetics can also lead to a deficiency in the enzymes that break-down histamines. The symptoms of histamine intolerance include: headaches/ migraines, mood changes, brain fog, acid reflux, nausea, bloating, diarrhea or constipation, heart arrhythmia, dizziness, sinus congestion, skin reactions, insomnia, and other sleep difficulties.

Foods high in histamine include:

Alcohol, fermented beverages, fermented foods, cheese (except: cream cheese, mozzarella, ricotta, and gouda), dried fruits, avocados, balsamic vinegar, bamboo shoots, bananas, plantains, beef jerky, bell pepper, black pepper, buckwheat, chili pepper, cocoa, cumin, curry, diet soda, egg plant, egg whites, garbanzo beans, garlic, grapefruit, green beans, horseradish, kiwi, lemons and limes, lima beans, mandarins, mushrooms, mustard, olives, oranges, parsnips, peanuts, pears, pickles, pineapple, plums, potatoes, pork bratwursts, processed meats, prosciutto, salami, sea vegetables, sauerkraut, soybeans, spinach, strawberries, sunflower seeds, tangerines, tomatoes, tuna, walnuts, yeast extract. Any other food allergies an individual might have will also raise their histamine levels.
Note: To reduce your symptoms of histamine imbalance, reduce your consumption of the above foods.  In addition, methyl groups added to your supplement program can help the body increase the production of histamine.  In fact, measurement of whole blood histamine indicates low levels of methyl groups.