Definition and causes of allergic rhinitis

Rhinitis is an inflammation of the mucosal lining of the nose. Rhinitis is classified as:

• allergic rhinitis
• infectious rhinitis—see Acute rhinosinusitis for management
• nonallergic rhinitis (also called vasomotor rhinitis)—no identifiable allergic trigger or infective cause
• occupational rhinitis—caused by workplace irritants (eg cleaning chemicals, foods)
• drug-induced rhinitis—causes include aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs), vasodilator drugs (eg some antihypertensives), intranasal decongestants (causing rhinitis medicamentosa) and estrogen-containing preparations (including combined oral contraceptives).

Allergic rhinitis is the most common form of rhinitis; it affects around 19% of the population in Australia. Common symptoms of allergic rhinitis include rhinorrhoea, sneezing, nasal blockage, nasal itch and, occasionally, altered sense of smell. Allergic conjunctivitis often coexists with allergic rhinitis.

Allergic rhinitis is associated with an immunoglobulin E (IgE)-mediated immune response to environmental allergens. The allergens can be seasonal (eg grass, weed and tree pollens) or perennial (eg dust mites, cat and dog dander). Symptoms can be further aggravated by chemical irritants (eg smoking, including exposure to second-hand smoke).

Allergic rhinitis and asthma commonly coexist (sometimes referred to as ‘United Airway Disease’)—asthma occurs in 30% of patients with allergic rhinitis, and allergic rhinitis occurs in more than 80% of patients with allergic asthma. Always assess patients with rhinitis for coexisting asthma (see Asthma diagnosis).

Allergic rhinitis also commonly coexists with sinusitis (see Chronic rhinosinusitis) and atopic dermatitis.

Patients with allergic rhinitis and rye grass sensitisation are at increased risk of thunderstorm asthma. Always assess patients with allergic rhinitis who live in an area with high rye grass pollen levels for risk of thunderstorm asthma—see here for more information.

While most rhinitis is allergic, a patient history can help identify other possible types of rhinitis before starting treatment for allergic rhinitis. Features that suggest an alternative diagnosis include unilateral symptoms, nasal obstruction without other symptoms, pain, purulent discharge, recurrent epistaxis and loss of sense of smell.