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Allergic rhinitis (hay fever) is a condition that affects an estimated 20 percent of Americans every year, according to the American College of Allergy, Asthma and Immunology. The condition is an allergy-induced inflammation of the nasal passages, throat and eyes. This is caused by certain trigger proteins found in airborne substances such as pollens and molds.

Non-allergic rhinitis produces symptoms similar to allergic rhinitis. However, it is actually caused by viruses or irritants (e.g., cigarette smoke, pollution, fragrances, paint fumes) and is not triggered by allergens. Because of the similarities, it may be difficult to distinguish between the two.

Because many types of pollen vary by season, allergic rhinitis is worse in the spring and mid to late summer for many people. However, those people who are allergic to indoor allergens such as dust mites, mold and animal dander often experience symptoms year-round.

Geography can also play a role in the timing and severity of rhinitis symptoms. Some plants pollinate later in the year if they are located farther to the north (or farther to the south in the Southern Hemisphere). For example, grasses in the north will often pollinate later in the spring or summer than grasses in the south because of the milder southern winters. Ragweed pollen is the main culprit in about 75 percent of allergic rhinitis cases. Ragweed appears in all parts of the United States in varying levels. It is less prevalent west of the Rockies.

Allergic rhinitis occurs when an airborne allergen gains access to the body, usually through the nose (though sometimes through ingestion or skin contact). To ward off the proteins in the allergen that the immune system has misidentified as a threat, IgE antibodies are produced. The IgE triggers the body’s mast cells, which in turn release powerful chemicals, such as histamines and leukotrienes. This sequence of events is known as an allergic cascade.

Histamines are directly responsible for most of the symptoms associated with an allergy. They cause itching, swelling and fluid leaking from cells, particularly in the tissues of the nose, skin, throat and lungs. In allergic rhinitis, the effects of histamines can be localized in specific areas, such as the:

• Nose and nasal passages (rhinitis)
• Sinuses (sinusitis)
• Paranasal sinuses, adjacent to the nose (rhinosinusitis)
• Tissues around the eye (conjunctivitis)

Histamine causes liquid to be produced in the membranes of the nose and sinuses (by dilating the small blood vessels located there). This causes mucus to form in the nose and sinuses, leading to congestion and sneezing. Histamine also causes tissues to swell in the nose and sinuses, which can further interfere with nasal and sinus function. Mucus dripping from the back of the nose and into the upper throat (known as postnasal drip) can cause coughing and sore throat.

The nasal tissues often go through a cycle of congestion and decongestion that lasts for several hours. People may experience nasal congestion switching back and forth along this cycle. If the congestion in the sinuses becomes severe enough, facial pressure and pain are often the result. Allergic rhinitis is often accompanied by allergic sinusitis, allergic rhinosinusitis and/or allergic conjunctivitis.

People with a family history of allergies are more likely to develop allergic rhinitis, particularly those people with other allergy-related conditions, such as eczema and asthma. Although allergic rhinitis can develop at any age, it usually appears in individuals before the age of 30.

Uncontrolled, allergic rhinitis can seriously impair quality of life. It can interfere with sleep, resulting in daytime sleepiness, and affect the ability to learn and perform tasks. In addition, untreated or improperly treated allergic rhinitis may eventually lead to other complications. These include chronic ear infections (otitis media) and ear dysfunction. Nasal polyps have also been associated with allergic rhinitis, though the connection is unclear.

The severity of allergic rhinitis symptoms usually improve as a patient ages. However, the condition can worsen over time in some people.