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 or tree 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 it does not cause a fever. 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 (coumarin). A competing popular name was 'hay asthma'.
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 identified the condition of hay fever in 1819, believing it to be a disease. The true agent causing hay fever was finally identified as pollen in 1859 by Charles Blackley, who concluded that pollen contained toxins leading to the reaction. It was not until 1906 that the mechanisms of allergy as a type of hypersensitivity were understood following the work of Clemens von Pirquet.
Allergies are common. Heredity and environmental exposures may contribute to a predisposition to allergies. It is roughly estimated that one in three people has 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.
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, 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 (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.
Sufferers 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 range of 37.5–38.3 °C (99.5-100.9 °F). However, the name still makes some sense because it can cause increased fluctuation in the core temperature of a sufferer, in conjunction with inflammation.
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 allergic rhinitis throughout the year. The pollen that causes hay fever varies between individuals and from region to region; in general, 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 common 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 Vulgaris), Fat hen (Chenopodium), and sorrel/dock (Rumex)
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 a patch test to determine if a particular substance is causing the rhinitis, or an intradermal, scratch, or other test. Less commonly, the suspected allergen is dissolved and dropped onto the lower eyelid as a means of testing for allergies. This test should be done only by a physician, never the patient, since it can be harmful if done improperly. In some individuals not able to 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 are not 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 that do not have symptoms to that allergen.
Even if a person has negative skin-prick, intradermal and blood tests for allergies, he/she 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.
Allergic rhinitis may be seasonal or perennial. Seasonal allergic rhinitis occurs in particular 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.
The goal of rhinitis treatment is to prevent or reduce the symptoms caused by the inflammation of affected tissues. Measures that 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.
Antihistamine drugs can be taken orally and nasally to control symptoms such as sneezing, rhinorrhea, itching, and conjunctivitis.
It is best to take oral antihistamine medication before exposure, especially for seasonal allergic rhinitis. In the case of nasal antihistamines like azelastine antihistamine nasal spray, relief from symptoms is experienced within 15 minutes allowing for a more immediate 'as-needed' approach to dosage.
Antihistamine drugs can have undesirable side-effects, the most notable one being drowsiness in the case of oral antihistamine tablets. First-generation antihistamine drugs such as diphenhydramine cause drowsiness, but second- and third-generation antihistamines such as cetirizine and loratadine are less likely to cause drowsiness.
Pseudoephedrine is also indicated for vasomotor rhinitis. It is used only 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 in effort to prevent the making of methamphetamine.
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 must be taken continuously 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.
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.
Allergen immunotherapy (AIT, also termed desensitization) treatment involves administering doses of allergens to accustom the body to substances that are generally harmless (pollen, house dust mites), thereby inducing specific long-term tolerance. Allergy immunotherapy can be administered orally (as sublingual tablets or sublingual drops), or by injections under the skin (subcutaneous). Discovered by Leonard Noon and John Freeman in 1911, allergy immunotherapy represents the only causative treatment for respiratory allergies.
Complementary and alternative treatments
Therapeutic efficacy of complementary-alternative treatments such as acupuncture and homeopathy is not supported by currently available evidence. Some evidence shows that acupuncture is effective for rhinitis, whereas 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 serious otitis media and orthodontic problems. Patients of nasal allergy have four times more risk of developing 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 having 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.
Vaccination against Influenza viruses, Adenoviruses, Measles, Rubella, Streptococcus pneumoniae, Haemophilus influenzae, Diphtheria, Bacillus anthracis, and Bordetella pertussis may even help prevent allergic rhinitis, and possible complication of asthma.
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