17.03.1 Introduction

Rhinitis is the acute or chronic inflammation of the nasal mucosa causing itching and sneezing. Rhinorrhea is excessive watery nasal secretions (a runny nose). Rhinitis and rhinorrhea are caused by either viral infections (e.g. the common cold) or allergic reactions, such as seasonal allergies (e.g. hayfever) or chronic/perennial allergies (e.g. dust mites, animal dander). Allergic rhinitis is suffered from by 1 in 5 people and this affects their quality of life, and reduces school and work performance. Unlike in the allergic condition asthma, where histamine only has a minor role, histamine is a major mediator of rhinitis. Histamine H₁-receptor antagonists counter the rhinitis.

In rhinitis there is nasal vasodilation and increased blood vessel permeability (oedema) leading to an enlargement of nasal mucosa, which causes difficulty with inspiration of air (difficulty breathing through the nose). Activation of the sympathetic nervous system causes vasoconstriction in the nasal mucosa, decreases blood vessel permeability, which in turn reduces the nasal mucosa size, and improves the ability to inspire through the nose. Thus, sympathomimetics are useful in nasal rhinitis and congestion