Histamine intolerance is quite simply an imbalance of histamine and the enzyme DAO in the body.
Histamine plays a vital role in the human body, most importantly as the body's natural defense against many types of infection. It acts as a neurotransmitter, sending warning signals around the body and helping the immune system to fight off unwanted attacks, using by provoking an inflammatory response. While most of the time this process goes relatively unnoticed, and indeed helps you stay healthy, many people can develop histamine intolerance.
The way histamine usually works is by causing blood vessels to dilate, allowing blood cells to quickly locate and deal with any infection, but when the body doesn't break down this histamine, a build up occurs, and can trigger unwanted side effects or intolerance. This intolerance can manifest itself in many ways, and affect many different areas of the body, including the skin, brain, lungs or the cardiovascular system - this causes a wide range of symptoms and problems which need to be dealt with; some of these may prove difficult to diagnose.
A relatively common way in which histamine intolerance presents is following the consumption of foods which release histamine in large amounts - these can include aged cheeses or meats, milk, eggs, chocolate and many common foods. The intake of a large amount of histamine can cause a range of symptoms, which may include a nasty skin rash, bad headaches or other inflammation. High levels of histamine can also result from many other sources, such as a bacterial overgrowth, food or other allergies, and drinking too much fermented alcohol.
Once histamine has been generated, it is usually broken down enzymes in the body. The most prevalent of these is diamine oxidase (DAO), the chemical enzyme which naturally breaks down histamine in the digestive tract. The action of DAO to reduce histamine levels can be blocked by the consumption of some foods. These include black and green teas, various forms of alcohol and even certain energy drinks. Similarly, a natural DAO deficiency may often be directly linked to, or cause, histamine intolerance. The consumption of food itself doesn't necessarily cause a histamine intolerance to appear instantly, there is usually a cumulative effect which is gradually built up and which triggers once the body's histamine level hits a certain trigger point.
Histamine intolerance reportedly affects around 1% of the world's population, and is particularly prevalent in middle aged and older people - females can be particularly prone to a histamine intolerance, due to a link between histamine production and estrogen levels; periods of menstruation can go together with bouts of histamine intolerance due to the raised levels of both chemicals.