It seems that some of us make way more histamine than is necessary for typical bodily functions. I personally have been told by numerous doctors over the years that I "just have a lot of histamine" and that antihistamines are "like a drop in the bucket" for me. Another favorite phrase of the doctors I have seen is "come back if it gets worse."
I apparently am not alone.
There are several ways that a person can make too much histamine on a continuous or regular basis. The first mechanism is fairly well understood: you have allergies. When your body encounters something like dust, or pollen, a cat, or you eat strawberries, peanuts, milk and your body produces histamine. Allergists will then recommend that you receive allergy shots and take antihistamines. When you avoid your various allergy triggers you generally feel pretty good.
For others, allergic like symptoms occur with no known cause or there seem to be a widely varying amount of causes. In recent medical history mast cells have been determined to be the intimately involved in these phenomena. Mast cells are a member of the immune system and store histamine and many other hormonal mediators. When they are activated, mast cells release these components and start a wide variety of immune related processes.
Mast cells can cause too much histamine to be present in two related ways. In one instance, the body makes too many mast cells, some of which are atypically formed, and those atypically formed cells can be activated in aberrant (not normal) ways. The classification of this disease process is referred to as mastocytosis. For others, the appropriate amount of mast cells are present in the body but those mast cells can also inappropriately release their contents and activate the allergic pathway. People in this camp are currently classified as having a Mast Cell Activation Disorder, Disease or Syndrome.
In both Mastocytosis and Mast Cell Activation Disorders, symptoms wax and wane over time for apparently no reason. Various benign things (a scent, stress, heat or cold, etc) can cause a local or systemic "allergic" reaction.