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Allergic rhinitis, also known as hay fever or pollinosis, is a condition which occurs when the immune system overreacts to allergens in the air. Signs and symptoms include a runny or stuffy nose, sneezing, red, itchy, and watery eyes, and swelling around the eyes. The fluid from the nose is usually clear. Symptoms onset is often within minutes following exposure and they can affect sleep, the ability to work, and the ability to concentrate at school.〔 Those whose symptoms are due to pollen typically develop symptoms during specific times of the year.〔 Many people with allergic rhinitis also have asthma, allergic conjunctivitis, or atopic dermatitis. Allergic rhinitis is typically triggered by environmental allergens such as pollen, pet hair, dust, or mold. Inherited genetics and environmental exposures contribute to the development of allergies. Growing up on a farm and having multiple siblings decreases the risk. The underlying mechanism involved IgE antibodies attaching to the allergen and causing the release of inflammatory chemicals such as histamine from mast cells.〔 Diagnosis is usually based on a medical history in combination with a skin prick test or blood tests for allergen-specific IgE antibodies. These tests, however, are sometimes falsely positive. The symptoms of allergies resemble those of the common cold; however, they often last for more than two weeks and typically do not include a fever.〔 Exposure to animals in early life might reduce the risk of developing allergies to them later.〔 A number of medications may improve symptoms including nasal steroids, antihistamines such as diphenhydramine, cromolyn sodium, and leukotriene receptor antagonists such as montelukast. Medications are, however, not sufficient or associated with side effects in many people.〔 Exposing people to larger and larger amounts of allergen, known as allergen immunotherapy is often effective. The allergen may be given as injections just under the skin or as a tablet under the tongue. Treatment typically lasts three to five years after which benefits may be prolonged.〔 Allergic rhinitis is the type of allergy that affects the greatest number of people.〔 In Western countries, between 10–30% of people are affected in a given year.〔 It is most common between the ages of twenty and forty.〔 The first accurate description is from the 10th century physician Rhazes. Pollen was identified as the cause in 1859 by Charles Blackley. While in 1906 that the mechanisms was determined by Clemens von Pirquet. 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. ==Signs and symptoms== The characteristic symptoms of allergic rhinitis are: rhinorrhea (excess nasal secretion), itching, sneezing fits, and nasal congestion and obstruction.〔 Characteristic physical findings include conjunctival swelling and erythema, eyelid swelling, lower eyelid venous stasis (rings under the eyes known as "allergic shiners"), swollen nasal turbinates, and middle ear effusion. There can also be behavioural signs; in order to relieve the irritation or flow of mucus, people may wipe or rub their nose with the palm of their hand in an upward motion: an action known as the "nasal salute" or the "allergic salute". This may result in a crease running across the nose (or above each nostril if only one side of the nose is wiped at a time), commonly referred to as the "transverse nasal crease", and can lead to permanent physical deformity if repeated enough. People might also find that cross-reactivity occurs. For example, someone allergic to birch pollen may also find that he/she has an allergic reaction to the skin of apples or potatoes. A clear sign of this is the occurrence of an itchy throat after eating an apple or sneezing when peeling potatoes or apples. This occurs because of similarities in the proteins of the pollen and the food. There are many cross-reacting substances. Hay fever is not a true fever, meaning it does not cause a core body temperature in the fever over 37.5–38.3 °C (99.5-100.9 °F). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Allergic rhinitis」の詳細全文を読む スポンサード リンク
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