Pollen grains from a variety of common plants can cause hay fever. Enlarged 500×, ~400 µm wide.
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Allergic rhinitis is an allergic inflammation of the nasal airways. It occurs when an allergen, such as pollen, dust or animal dander (particles of shed skin and hair) is inhaled by an individual with a sensitized immune system. In such individuals, the allergen triggers the production of the antibody immunoglobulin E (IgE), which binds to mast cells and basophils containing histamine. When caused by pollens of any plants, it is called pollinosis, and if specifically caused by grass pollens, it is known as hay fever. While symptoms resembling a cold or flu can be produced by an allergic reaction to pollen from plants and grasses, including hose used to make hay, it does not cause a fever.
IgE bound to mast cells are stimulated by allergens, causing the release of inflammatory mediators such as histamine (and other chemicals). This usually causes sneezing, itchy and watery eyes, swelling and inflammation of the nasal passages, and an increase in mucus production. Symptoms vary in severity between individuals. Very sensitive individuals can experience hives or other rashes. Particulate matter in polluted air, and chemicals such as chlorine and detergents, which can normally be tolerated, can greatly aggravate allergic rhinitis. The physician John Bostock first described hay fever in 1819 as a disease.
Allergies are common. Heredity and environmental exposures may contribute to a predisposition to allergies. It is roughly estimated that one in three people have an active allergy at any given time and at least three in four people develop an allergic reaction at least once in their lives. In Western countries between 10–25% of people annually are affected by allergic rhinitis.
Allergic rhinitis may be seasonal or perennial. Seasonal allergic rhinitis occurs particularly during pollen seasons. It does not usually develop until after 6 years of age. Perennial allergic rhinitis occurs throughout the year. This type of allergic rhinitis is commonly seen in younger children.
Allergic rhinitis may also be classified as Mild-Intermittent, Moderate-Severe intermittent, Mild-Persistent, and Moderate-Severe Persistent. Intermittent is when the symptoms occur <4 days per week or <4 consecutive weeks. Persistent is when symptoms occur >4 days/week and >4 consecutive weeks. The symptoms are considered mild with normal sleep, no impairment of daily activities, no impairment of work or school, and if symptoms are not troublesome. Severe symptoms result in sleep disturbance, impairment of daily activities, and impairment of school or work.
Signs and symptoms 
The characteristic symptoms of allergic rhinitis are: rhinorrhea (excess nasal secretion), itching, 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, patients 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, commonly referred to as the "transverse nasal crease", and can lead to permanent physical deformity if repeated enough.
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 or apples. This occurs because of similarities in the proteins of the pollen and the food. There are many cross-reacting substances.
Allergy testing 
Allergy testing may reveal the specific allergens to which an individual is sensitive. 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 some individuals who cannot undergo skin testing (as determined by the doctor), the RAST blood test may be helpful in determining specific allergen sensitivity. Peripheral eosinophilia can be seen in differential leukocyte count.
Allergy testing can either show allergies that aren't actually causing symptoms, or miss allergies that do cause symptoms. The intradermal allergy test is more sensitive than the skin prick test but is more often positive in people who do not have symptoms to that allergen.
Even if a person has negative skin-prick, intradermal and blood tests for allergies, they may still have allergic rhinitis, from a local allergy in the nose. This is called local allergic rhinitis. Specialized testing is necessary to diagnose local allergic rhinitis.
Pollen allergies 
Allergic rhinitis triggered by the pollens of specific seasonal plants is commonly known as "hay fever", because it is most prevalent during haying season. However, it is possible to suffer from hay fever throughout the year. The pollen which causes hay fever varies between individuals and from region to region; generally speaking, the tiny, hardly visible pollens of wind-pollinated plants are the predominant cause. Pollens of insect-pollinated plants are too large to remain airborne and pose no risk. Examples of plants commonly responsible for hay fever include:
- Trees: such as pine (Pinus), birch (Betula), alder (Alnus), cedar, 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. A major antigen in these is a protein called Bet V I. Olive pollen is most predominant in Mediterranean regions. Hay fever in Japan is caused primarily by sugi (Cryptomeria japonica) and hinoki (Chamaecyparis obtusa) tree pollen.
- Grasses (Family Poaceae): especially ryegrass (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)
The goal of rhinitis treatment is to prevent or reduce the symptoms caused by the inflammation of affected tissues. Measures which are effective include avoiding the allergen. Intranasal corticosteroids are the preferred treatment if medications are required with other options used only if these are not effective. Mite proof covers, air filters, and withholding certain foods in childhood do not have evidence supporting their effectiveness.
Intranasal corticosteroids are used to control symptoms associated with sneezing, rhinorrhea, itching and nasal congestion. It is an excellent choice for perennial rhinitis. Steroid nasal sprays are effective and safe, and may be effective without oral antihistamines. They take several days to act and so need be taken continually for several weeks as their therapeutic effect builds up with time.
Systemic steroids such as prednisone tablets and intramuscular triamcinolone acetonide injection are effective at reducing nasal inflammation, but their use is limited by their short duration of effect and the side effects of prolonged steroid therapy.
Antihistamine drugs can have undesirable side-effects, most notably drowsiness. First generation antihistamine drugs such as diphenhydramine cause drowsiness, but second- and third-generation antihistamines such as cetirizine and loratadine do not.
Antihistamine drugs can be taken orally to control symptoms such as sneezing, rhinorrhea, itching and conjunctivitis. It is best to take the medication before exposure, especially for seasonal allergic rhinitis. Ophthalmic antihistamines (such as ketotifen) are used for conjunctivitis; intranasal forms are used for sneezing, rhinorrhea and nasal pruritus.
Pseudoephedrine is also indicated for vasomotor rhinitis. It is only used when nasal congestion is present and can be used with antihistamines. In the United States, oral decongestants containing pseudoephedrine must be purchased behind the pharmacy counter by law to combat the making of methamphetamine.
Topical decongestants may 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 called rhinitis medicamentosa.
More severe cases of allergic rhinitis not responding to medication may benefit from allergen immunotherapy (allergy shots). Allergen is given in gradually increasing doses until a maintenance dose is reached. Immunotherapy suppresses the formation of IgE and raises the titre of IgE antibody. Immunotherapy has to be given for a year before significant improvement of symptoms can be noticed. It is discontinued if uninterrupted treatment for five years shows no clinical improvement.
Alternative treatments 
Therapeutic efficacy of complementary-alternative treatments is not supported by currently available evidence. Some evidence shows that acupuncture is effective for rhinitis while other evidence does not. The overall quality of evidence, however, is poor.
Nasal allergy may cause recurrent sinusitis because of the obstruction to the sinus ostia. It may lead to the formation of nasal polypi. Nasal allergy can result in serous otitis media and orthodontic problems. Patients of nasal allergy have four times more risk of developing bronchial asthma.
Local allergic rhinitis 
Local allergic rhinitis is an allergic reaction in the nose to an allergen, without systemic allergies. So skin-prick and blood tests for allergy are negative, but there are IgE antibodies produced in the nose that react to a specific allergen. Intradermal skin testing may also be negative.
The symptoms of local allergic rhinitis are the same as the symptoms of allergic rhinitis, including symptoms in the eyes. Just as with allergic rhinitis, people can have either seasonal or perennial local allergic rhinitis. The symptoms of local allergic rhinitis can be mild, moderate or severe. Local allergic rhinitis is associated with conjunctivitis and asthma.
In one study, about 25% of patients with rhinitis had local allergic rhinitis. In several studies, over 40% of people who had been diagnosed with nonallergic rhinitis were found to actually have local allergic rhinitis.
Steroid nasal sprays and oral antihistamines have been found to be effective for local allergic rhinitis. A preliminary study found that allergy shots were also effective, and clinical trials of allergy shots are being done, as of Dec. 2012.
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- Allergy Friendly Trees
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