Hay fever

 ICD9        = 477|

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For the play, see Hay Fever

Allergic rhinitis, also called pollinosis, hay fever or nasal allergies, is a collection of symptoms, predominantly in the nose and eyes, that occur after exposure to airborne particles of dust, dander, or the pollensof certain seasonal plants in people who are allergicto these substances.

When these symptoms are caused by pollens, the allergic rhinitis is commonly known as "hay fever", after the fact it is most prevalent during haying.

Causes

Allergies are caused by an oversensitive immune system, leading to a misdirected immune response. The immune system normally protects the body against harmful substances such as bacteriaand viruses. Allergy occurs when the immune system reacts to substances (allergens) that are generally harmless and in most people do not cause an immune response.

As noted above, hay fever involves an allergic reactionto pollen. A virtually identical reaction occurs with allergy to mold, animal dander, dust, and similar inhaled allergens. Particulate matter in polluted air and chemicals such as chlorine and detergents, which can normally be tolerated, can greatly aggravate the condition.

The pollens that cause hay fever vary from person to person and from region to region; generally speaking, the tiny, hardly visible pollens of wind-pollinatedplantsare the predominant culprits. Pollens of insect-pollinatedplants are too large to remain airborne and pose no risk. Examples of plants commonly responsible for hay fever include:

• Trees: such as birch (Betula), alder (Alnus), hazel (Corylus), hornbeam (Carpinus), horse chestnut (Aesculus), willow (Salix), poplar(Populus), plane (Platanus), linden/lime (Tilia) and olive (Olea). In northern latitudes birch is considered to be the most important allergenic tree pollen, with an estimated 15-20% of hay fever sufferers sensitive to birch pollen grains. Olive pollen is more important in Mediterranean regions.
• Grasses (Family Poaceae): especially rye(Lolium sp.) and timothy(Phleum pratense). An estimated 90% of hay fever sufferers are allergic to grass pollen.
• Weeds:ragweed(Ambrosia), plantain (Plantago), nettle/parietaria(Urticaceae), mugwort(Artemisia), Fat hen(Chenopodium) and sorrel/dock (Rumex)

In addition to individual sensitivity and geographic differences in local plant populations, the amount of pollen in the air can be a factor in whether hay fever symptoms develop. Hot, dry, windy days are more likely to have increased amounts of pollen in the air than cool, damp, rainy days when most pollen is washed to the ground.

When an allergen such as pollen or dust is inhaled by a person with a sensitized immune system, it triggers antibodyproduction. These antibodies bind to cells that contain histamine. When the antibodies are stimulated by pollen and dust, histamine (and other chemicals) are released. This causes itching, swelling, and mucusproduction. Symptoms vary in severity from person to person. Very sensitive individuals can experience hivesor other rashes.

Some disorders may be associated with allergies. These include eczemaand asthma, among others.

Allergies are common. Heredity and environmental exposures may contribute to a predisposition to allergies.

Symptoms

• coughing
• headache
• itchingnose, mouth, eyes, throat, skin, or any area
• runny nose(and occasionally nosebleeds)
• impaired smell
• sneezing
• stuffy nose (nasal congestion)
• tearing eyes
• sore throat
• wheezing
• cross-reactivity allergyto certain fruits

Signs and tests

The history of the person's symptoms is important in diagnosing allergic rhinitis, including whether the symptoms vary according to time of day or the season; exposure to pets or other allergens; and dietchanges.

Allergy testing may reveal the specific allergens the person is reacting to. Skin testing is the most common method of allergy testing. This may include intradermal, scratch, patch, or other tests. Less commonly, the suspected allergen is dissolved and dropped onto the lower eyelid as a means of testing for allergies. (This test should only be done by a physician, never the patient, since it can be harmful if done improperly.)

In certain individuals who cannot undergo skin testing (as determined by the doctor), the RAST blood testmay be helpful in determining specific allergen sensitivity.

Sufferers might also find that cross-reactivity occurs. For example, someone allergic to birch pollen may also find that they have 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. This occurs because of similarities in the proteins of the pollen and the food. There are many cross-reacting substances.

Treatment

The goal of treatment is to reduce allergy symptoms caused by the inflammation of affected tissues. The best "treatment" is to avoid what causes your allergic symptoms in the first place.

Medication

The most appropriate medication depends on the type and severity of symptoms. Specific illnesses that are caused by allergies (such as asthma and eczema) may require other treatments.

Options include the following:

• Short-acting antihistamines, which are generally over-the-counter (non-prescription), often relieve mild to moderate symptoms, but can cause drowsiness. A pediatrician should be consulted before using these medicines in children, as they may affect learning. One formerly prescription medication, loratadine(Claritin®), is now available over the counter in many countries. It does not tend to cause drowsiness or affect learning in children. Azelastin hydrocholoride(Astelin®) is the only anitihistamine available as a nasal spray.
• Longer-acting antihistamines cause less drowsiness, can be equally effective, and usually do not interfere with learning. These medications include fexofenadine(Allegra), and cetirizine(Zyrtec).
• Corticosteroidnasal spraysare effective and somewhat safe, and may be effective without oral antihistamines. These medications include fluticasone(Flonase/Flixonase), budesonide(Rhinocort), mometasone(Nasonex), triamcinolone(Nasacort) and beclomethasone(Beconase®).
• Topical decongestantsmay also be helpful in reducing symptoms such as nasal congestion, but should not be used for long periods as stopping them after protracted use can lead to a rebound nasal congestion (Rhinitis medicamentosa).
• Cromolyn sodium(or cromoglycate) is available as a nasal spray (Nasalcrom) for treating hay fever. Eye drop versions of cromolyn sodium are available for allergic conjunctivitis.
• "Allergy shots" (Hyposensibilization, immunotherapy) are occasionally recommended if the allergen cannot be avoided and if symptoms are hard to control. This includes regular injections of the allergen, given in increasing doses (each dose is slightly larger than the previous dose) that may help the body adjust to the antigen.

Expectations

Most symptoms of allergic rhinitis can be readily treated.

In some cases (particularly children), people may outgrow an allergy as the immune system becomes less sensitive to the allergen. However, as a general rule, once a substance causes allergies for an individual, it can continue to affect the person over the long term.

More severe cases of allergic rhinitis require immunotherapy (allergy shots) or removal of tissue in the nose (e.g., nasal polyps) or sinuses.

Complications

• drowsinessand other side effects of antihistamines
• side-effectsof other medications(see the specific medication)
• sinusitis
• nasal polyps
• disruption of lifestyle (usually not severe)

External links

• Information on hay fever and childrenfrom Seattle Children's Hospital
• NIH site on Allergic Rhinitis
• Hay Fever and Rhinitis - National Asthma Campaign (UK)
• Cross-Reactivity Allergies
• eMedicine Health

de:Heuschnupfen nl:Hooikoorts [[pl:Katar ?>i?nny]] ja:花粉症 zh:花粉過敏症

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Hay+fever Wikipedia article Hay fever.