Causes of Rhinitis

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Rhinitis due to the common cold is caused by cold viruses and secondary infection with bacteria.

Allergic rhinitis is an allergic reaction to something, usually pollen, dust or animal hair and occurs when allergens trigger the release of histamine and other irritating substances.

Fundamental to an understanding of allergic rhinitis are the mast cells, these are cells full of granules of histamine and serotonin and other irritating substances. They are central to the allergic reaction and to many immune system processes. They are found in large numbers in the skin and mucous membranes and in the lymphatic system.

In people with allergies, a particular type of antibody is produced in unusually high numbers. This is the immunoglobulin type E (IgE). Like all antibodies, these are protein molecules. Large numbers of these molecules remain attached to the specific receptors on the surface of the mast cells.

When a pollen or other granule reaches the cell and bridges across between two or more IgE molecules, it causes a strain on the mast cell membrane, which tears, releasing its contents. Histamine causes the muscle in the walls of the air tubes of the lungs to tighten, arteries to widen, small blood vessels (capillaries) to leak, and skin to itch.

Allergic rhinitis is most commonly caused by grass pollen, but tree and weed pollens and mould spores can also cause attacks.