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When allergic rhinitis is suspected, the first step is usually to perform a physical examination and obtain a complete medical history. Obtaining the patient’s medical history is important because the presence of other allergies, asthma or eczema raises the likelihood of a person having allergic rhinitis. A family history where allergies are common is another factor that predisposes a person towards allergic rhinitis. Typically the family history will show instances of allergic rhinitis, asthma or other airborne allergies.

The physician will ask the patient about the type of symptoms being experienced, as well as the duration of the symptoms. A physician will also take into account the time of year when evaluating a patient. The symptoms of allergic rhinitis are often seasonal, with symptoms appearing more often during the time of year when pollens and molds are most present. While the allergy season can differ by geography, most people experience allergic flare-ups in the spring or summer.

Allergic rhinitis symptoms often mimic those of a cold (non-allergic rhinitis). For this reason, diagnosing allergic rhinitis can be difficult. Generally, allergy symptoms persist for a longer period of time than cold symptoms (more than seven days), and the mucus produced in the nose during a cold is thicker than with rhinitis. Itching of the ears, nose and throat may be associated with allergic rhinitis, though usually not a cold.

The physician will also inquire about the patient's home environment, work environment and hobbies. This will help the physician pinpoint the allergens that are triggering the symptoms.

Different types of rhinitis are triggered by different factors. Before a diagnosis of allergic rhinitis is made, physicians must be sure another type of rhinitis is not to blame. Changes in the weather, hormones in the individual or physical defects in the nasal septum (partition in the nasal cavity) can all cause rhinitis symptoms.

Once other potential causes of symptoms are ruled out, the next step in diagnosing allergic rhinitis is to identify the specific allergen triggering symptoms. The most common method of identifying allergens is skin testing. Trace amounts of a variety of different allergens are introduced to the patient’s skin. For each specific allergen, a different area of skin is used. When an area of skin reacts with a wheal or a raised red bump (skin rashes), the patient is likely allergic to that specific allergen.

Blood tests, such as a radioallergosorbent test (RAST Test), may be performed to measure the amount of IgE produced by a particular allergen. In addition, x-rays or other types of imaging tests may be performed to rule out other causes of rhinitis, such as possible structural abnormalities, or to detect complications caused by rhinitis.