Antihistamines have been around for some time now, and without them a great number of us would regularly suffer the symptoms of an allergic reaction with little or no relief. In order to understand how antihistamines work, we need to look at the mechanism that induces the production of histamine and its effect on body cells.

Histamine is produced as part of the body's immune response to the invasion of a foreign object. This could be in the form of a virus or bacteria, or it could be an innocuous substance like pollen, animal hairs or nuts. At the first sign of an invasion a battalion of white blood cells, called lymphocytes, produce antibodies which march through our system and attach themselves to other white blood cells, called mast cells. When a foreign substance or allergen attacks, it attaches itself to the antibodies, giving rise to the release of an armed force called histamine which helps destroy the invader. Unfortunately histamine causes symptoms

such as swelling of small blood vessels that supply the skin and mucous membranes, and the contraction of muscles in the gastrointestinal tract, to name just a few. This response is important in the attempt to destroy the invading foreign substance, but causes uncomfortable irritations like a runny nose and eyes, itching skin, or upset stomach.

Relief from these symptoms can be brought about by antihistamines which act on a variety of sites and systems throughout the body. They can even act on the brain by suppressing the coughing reflex, controlling nausea, or inducing sleep.

When histamine is released as a result of a foreign substance or injury, it attaches itself to receptors in the skin, blood vessels, nasal passages and airways, or in the stomach. Imagine these receptors as little cups on the surface of cells and the histamine as a small particle the same shape as the cup. When a histamine particle meets a cell's "cup" the two fit perfectly and the histamine sits neatly inside the "cup". This provokes inflammation of the skin cell or blood vessel cell that the histamine is attached to, thus starting an allergic reaction.

Now imagine antihistamine as a very clever substance with "particles" that are also the same shape as the little "cups" on the cells. The drug's "particles" fit neatly inside the cup shaped cell receptors, filling them so the histamine can no longer attach itself. The cells no longer become inflamed and an allergic reaction is prevented.

There are many different antihistamines, all with different shaped "particles" that fit different shaped "cups" on different cells, each bringing relief to a variety of allergies. But due to the nature of their modus operandi, antihistamines are more effective when taken before the onset of an allergic reaction (while the "cups" are still empty) rather than once an attack has already started and the "cups" are full with histamine. So when it comes to allergies, prevention, rather than cure, is the key.

Learn more about this author, Libbie Reed.
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