A person with rhinitis typically presents with sneezing, itching, nasal discharge (rhinorrhoea), and blockage. Most cases of allergic rhinitis are diagnosed by identifying its characteristic features and excluding infectious and irritant causes of rhinitis:

• Exclude infective rhinitis. An infective cause for rhinitis is more likely when:
• There is an acute onset of 1 week or less.
• There are typical features of an associated upper respiratory tract infection, such as cough, fever, or lymphadenopathy.
• Exclude irritant rhinitis. An irritant cause for rhinitis is more likely when symptoms follow a known physical or chemical irritant cause of rhinitis:
• Physical irritant rhinitis may follow changes in temperature or humidity, or occur with exercise.
• Chemical irritant rhinitis may follow exposure to volatile chemicals and odours.
• Allergic rhinitis and irritant rhinitis may coexist. When they do, irritant rhinitis tends to be more severe.
• Identify the characteristic features of allergic rhinitis. An allergic cause for rhinitis is more likely when:
• There is a personal or family history of atopy (asthma, eczema, or allergic rhinitis).
• Symptoms follow exposure to a known allergic cause of rhinitis:
• House dust mites — symptoms are worse on waking and are present year-round but may peak in autumn and spring.
• Animal dander — symptoms follow exposure to animal dander. Symptoms may be year-round or occasional, depending on exposure.
• Tree pollens — intermittent or chronic symptoms occur from early to late spring.
• Grass pollens — intermittent or chronic symptoms occur from late spring to early summer.
• Weed pollens — intermittent or chronic symptoms may occur from early spring to early autumn.
• Allergens encountered at work — intermittent or chronic symptoms tend to improve when the person is away from work at weekends and holidays.
• Rhinitis is associated with nasal itching.
• Symptoms settle following treatment with antihistamines or topical corticosteroids.
• Arrange allergy testing when it is not possible to distinguish clearly from the history the type of rhinitis present (infective, irritant or allergic) or the allergen causing allergic rhinitis.
• Refer for skin prick testing where this is available.
• If skin prick testing is not available send blood for serum total and specific IgE.
• When allergy testing is negative consider rarer causes for the rhinitis, including drug-induced rhinitis, hormonal rhinitis, and non-allergic rhinitis with eosinophilia syndrome. For further information, see Differential diagnosis.

Recommendations for diagnosing allergic rhinitis are based on expert opinion from an American review article [Quillen and Feller, 2006].

• Infective rhinitis. An infective cause for rhinitis is more likely when:
• There is an acute onset of 1 week or less.
• There are typical features of an associated upper respiratory tract infection, such as cough, fever, or lymphadenopathy.
• Irritant rhinitis. An irritant cause for rhinitis is more likely when symptoms follow a known physical or chemical irritant cause of rhinitis:
• Physical irritant rhinitis may follow changes in temperature and humidity, or exercise.
• Chemical irritant rhinitis may follow exposure to volatile chemicals and odours.
• Rarer causes of rhinitis include:
• Drug-induced rhinitis, which should be considered when symptoms follow the start of treatment with such drugs as angiotensin-converting enzyme inhibitors, beta-blockers, chlorpromazine, aspirin, and nonsteroidal anti-inflammatory drugs. Rebound symptoms may occur when stopping treatment with nasal decongestants.
• Hormonal rhinitis should be considered when symptoms coincide with pregnancy, starting the oral contraceptive pill, or hypothyroidism.
• Non-allergic rhinitis with eosinophilia syndrome is diagnosed only when other causes of rhinitis, including allergic rhinitis, have been excluded.
• Conditions that can mimic the symptoms of rhinitis:
• Structural or mechanical factors include deviated nasal septum, nasal polyps, hypertrophic turbinates, adenoidal hypertrophy, foreign bodies, and (rarely) nasal tumours.
• Systemic conditions include primary defects in mucus (e.g. cystic fibrosis), primary ciliary dyskinesia (Kartagener's syndrome), and granulomatous disease (e.g. Wegener's granulomatosis, sarcoidosis).

Information on the differential diagnosis of allergic rhinitis is based on expert opinion from an American review article [Quillen and Feller, 2006].