Allergic rhinitis
Nasal inflammation due to allergens in the air / From Wikipedia, the free encyclopedia
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Allergic rhinitis, of which the seasonal type is called hay fever, is a type of inflammation in the nose that occurs when the immune system overreacts to allergens in the air.[6] Signs and symptoms include a runny or stuffy nose, sneezing, red, itchy, and watery eyes, and swelling around the eyes.[1] The fluid from the nose is usually clear.[2] Symptom onset is often within minutes following allergen exposure, and can affect sleep and the ability to work or study.[2][8] Some people may develop symptoms only during specific times of the year, often as a result of pollen exposure.[3] Many people with allergic rhinitis also have asthma, allergic conjunctivitis, or atopic dermatitis.[2]
| Allergic rhinitis | |
|---|---|
| Other names | Hay fever, pollenosis |
 | |
| SEM Microscope image of Pollen grains from a variety of common plants: sunflower (Helianthus annuus), morning glory (Ipomoea purpurea), prairie hollyhock (Sidalcea malviflora), oriental lily (Lilium auratum), evening primrose (Oenothera fruticosa), and castor bean (Ricinus communis). | |
| Specialty | Allergy and immunology |
| Symptoms | Stuffy itchy nose, sneezing, red, itchy, and watery eyes, swelling around the eyes, itchy ears[1] |
| Usual onset | 20 to 40 years old[2] |
| Causes | Genetic and environmental factors[3] |
| Risk factors | Asthma, allergic conjunctivitis, atopic dermatitis[2] |
| Diagnostic method | Based on symptoms, skin prick test, blood tests for specific antibodies[4] |
| Differential diagnosis | Common cold[3] |
| Prevention | Exposure to animals early in life[3] |
| Medication | Nasal steroids, antihistamines such as diphenhydramine, cromolyn sodium, leukotriene receptor antagonists such as montelukast, allergen immunotherapy[5][6] |
| Frequency | ~20% (Western countries)[2][7] |
Allergic rhinitis is typically triggered by environmental allergens such as pollen, pet hair, dust, or mold.[3] Inherited genetics and environmental exposures contribute to the development of allergies.[3] Growing up on a farm and having multiple siblings decreases this risk.[2] The underlying mechanism involves IgE antibodies that attach to an allergen, and subsequently result in the release of inflammatory chemicals such as histamine from mast cells.[2] It causes mucous membranes in the nose, eyes and throat to become inflamed and itchy as they work to eject the allergen.[9] Diagnosis is typically based on a combination of symptoms and a skin prick test or blood tests for allergen-specific IgE antibodies.[4] These tests, however, can give false positives.[4] The symptoms of allergies resemble those of the common cold; however, they often last for more than two weeks and, despite the common name, typically do not include a fever.[3]
Exposure to animals early in life might reduce the risk of developing these specific allergies.[3] Several different types of medications reduce allergic symptoms, including nasal steroids, antihistamines, such as diphenhydramine, cromolyn sodium, and leukotriene receptor antagonists such as montelukast.[5] Oftentimes, medications do not completely control symptoms, and they may also have side effects.[2] Exposing people to larger and larger amounts of allergen, known as allergen immunotherapy (AIT), is often effective.[6] The allergen can be given as an injection under the skin or as a tablet under the tongue.[6] Treatment typically lasts three to five years, after which benefits may be prolonged.[6]
Allergic rhinitis is the type of allergy that affects the greatest number of people.[10] In Western countries, between 10 and 30% of people are affected in a given year.[2][7] It is most common between the ages of twenty and forty.[2] The first accurate description is from the 10th-century physician Abu Bakr al-Razi.[11] In 1859, Charles Blackley identified pollen as the cause.[12] In 1906, the mechanism was determined by Clemens von Pirquet.[10] The link with hay came about due to an early (and incorrect) theory that the symptoms were brought about by the smell of new hay.[13][14] Although the scent per se is irrelevant, the correlation with hay checks out, as peak hay-harvesting season overlaps with peak pollen season, and hay-harvesting work puts people in close contact with seasonal allergens.