What is Histamine?

Histamine is the nemesis of people with allergies and the allergists that care for them.

Think of any allergic symptom and it is probably caused by histamine.  Histamine in the nose causes itching, sneezing, dripping, and congestion.  In the gastrointestinal system, it causes cramping pain, diarrhea, and vomiting.  In the skin, it causes itching, flushing, swelling, and hives.   
Where does the histamine come from? The answer is one of the more perplexing facts in medicine.  We make histamine.

We make histamine.

Histamine is manufactured and stored in a white blood cell called the mast cell.  In allergic reactions, the mast cells release histamine into the tissue or bloodstream.  The result is hives, hay fever, food allergy, and asthma.

Mast cells are part of our immune system and the primary job of our immune system is to protect us from invading viruses, bacteria, and parasites.   So then, why do our mast cells release a flood of histamine when we mow our grass lawn?  Or pet the cat?   Or eat a peanut?  The allergic reaction is a sophisticated, orchestrated, militaristic response to harmless elements in our environment, or in our food, or the medications we take, with potentially life-threatening consequences.  In all this, the primary weapon is histamine. 

Mast cells do play an important role in protecting us from pathogens.  They are very numerous in tissues that are exposed to the environment such as the respiratory tract, the skin, and the intestines, and have the ability to respond to dangerous elements such as infectious organisms and injury.  In this way, they play a role in what is called the innate immune response.  The sensors and response programming of the mast cell are hard-wired and ready to act even before birth.  The mast cell sensors can respond to certain “danger signals’ the first time it encounters it.  

It would be like a baby on the day it is born being able to act on an SOS in morse code by calling the coast guard.

When the mast cells sense danger they release a variety of chemicals stored inside the cell.  In addition to histamine, these chemicals begin the early inflammatory response, preparing the tissue and recruiting many other cells to the area that will complete the task.  Investigators have recently discovered evidence suggesting that mast cells may play a role in protecting us from honeybee, snake, lizard, and scorpion venoms.  

It may be that the powerful mast cell and histamine weapon system that now seems only to cause allergy problems may once have been crucial to the survival of our ancestors as they dealt with a more complex and threatening environment.