Allergic rhinitis is the predominant form of rhinitis in children, and accounts for about a third of adult rhinitis cases. Atopic individuals, with a family history of rhinitis, firstborn children and immigrants are predisposed to develop allergic rhinitis.
Allergic rhinitis is a response of the body’s immune system that interprets the presence of harmless allergen as a threat. Initial contact with allergens, such as grass pollen, at the nasal mucosa induces the formation of the antibody Immunoglobulin E (IgE). The next phase is known as sensitisation, which is when the IgE antibody becomes attached to nasal mast cells. These mast cells degranulate and immediately release mediators including histamine, prostaglandins and leukotrienes. It is the histamine which stimulates the sensory nerves and induces reflex sneezing and glandular hypersecretion. It also acts directly on the histamine receptors on blood vessels, causing vasodilatation (widening of the blood vessels) and oedema (accumulation of fluid beneath the skin). With prolonged allergen contact or high allergen exposure, a late-phase inflammatory reaction ensues with infiltration of cells, predominantly eosinophilia. The symptoms from this reaction are less obviously allergic: chronic nasal blockage, poor sense of smell, post-nasal catarrh and nasal hyper-reactivity.
* Mintel Press Release, “Not to be sneezed at – almost half of all Brits are allergy sufferers”, March 2010