Allergic rhinitis (AR), often called hay fever, is an inflammation of the nose by an allergic reaction to airborne substances. It is estimated that between 40 and 50 million people in the United States have allergies, and most of them had rhinitis as a symptom. Allergic rhinitis is more common in children than in adults and about 80% of cases develop before the age of 20.
There are two types of allergic rhinitis: seasonal and perennial. Seasonal AR occurs in the spring, summer and early fall when pollen in the atmosphere is at the highest level. Hay fever is caused by pollen from grass, trees, and mold spores. Symptoms of seasonal AR are worst after spending time outdoors in peak season.
Perennial AR occurs all year round and is usually caused by household or workplace air pollutants. The most common causes of are allergies to dust mites, animal dander, spores, cockroaches and indoor molds. In rare cases, allergic rhinitis is caused by food allergies. Some people may have multiple allergies with both seasonal and perennial causes.
Although allergies to a particular substance is not directly inherited, increased allergic sensitivity may have a genetic component. Allergic reactions are an immune system response. Normally, the immune system responds to foreign microorganisms or particles such as pollen or dust, by producing specific proteins called antibodies that are capable of binding to antigens of the foreign substance. This combination of antibodies and antigens starts a series of reactions designed to protect the body against possible infection.
The reaction that causes symptoms involves a special set of immune system cells called mast cells. These cells are found in the mucous membranes of the nose, eyes, Eustachian tubes, sinuses, and throat. On their surface, they display a special type of antibody called immunoglobulin type E (IgE). When a person inhales an allergen that they have sensitivity to, the allergen binds to the IgE on the mast cell. Mast cells store reactive chemicals in small packets, called granules. When the IgE antibodies encounter allergens, they trigger release of the granules, which release their chemicals and begin a complex set of biochemical reactions that involve neighboring cells, including blood vessels and nerve cells. One of these chemicals, histamine, binds to the surface of nearby cells that have special proteins known as histamine receptors on their surface. Interaction of histamine with receptors causes excess fluid collection, swelling, and increased redness, runny nose and red, irritated eyes characteristic of AR.
Grass and tree pollen most commonly cause seasonal AR, because their pollen is produced in large quantities and dispersed by the wind. Different plants give their pollen at different times of the year. Some people will suffer their worst symptoms in the spring while others will be affected more in the fall, depending on which plants can cause an allergic reaction.
Almost every type of tree or grass seasonally releases pollen that affects allergic rhinitis sufferers. Some of the more notorious offenders are: ragweed, pigweed, and tumbleweed. Perennial AR is often triggered by house dust, a complex mixture of airborne particles, many of which are strong allergens. House dust contains some or all of the following components: dust mites and their wastes, pet dander and mold spores.
Inflammation of the nose, or rhinitis, is the major and most complained about symptom of AR. Inflammation causes itching, sneezing, nasal discharge, and redness. Sinus swelling affects the inner ear and throat, causing a congested feeling. The drip of mucus from the sinuses down the back of the throat, combined with increased sensitivity, can also lead to throat irritation and redness. AR usually also causes redness, itching, and watery eyes. Fatigue and headache are also common.
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