Allergic rhinitis

Allergic rhinitis, also known as pollenosis or hay fever, 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.

IgE bound to mast cells are stimulated by pollen and dust, 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.

Classification
The two categories of allergic rhinitis include:
 * Seasonal&mdash;occurs particularly during pollen seasons. Seasonal allergic rhinitis does not usually develop until after 6 years of age.
 * Perennial&mdash;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. These symptoms may cause cough, cold or obstruction to respiratory passage while breathing.

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, lateral crease on the nose, swollen nasal turbinates, and middle ear effusion.

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.

Some disorders may be associated with allergies: Comorbidities include eczema, asthma and depression

Cause
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.

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, birch (Betula), alder (Alnus), cedar, hazel, hornbeam (Carpinus), horse chestnut (Aesculus), willow (Salix), poplar, 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 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)

Allergy testing may reveal the specific allergens an individual is sensitive 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 some individuals who cannot undergo skin testing (as determined by the doctor), the RAST blood test may be helpful in determining specific allergen sensitivity.

Management
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 use.

Steroids
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 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.

Other
Other measures that may be used second line include: antihistamines, decongestants, cromolyn, leukotriene receptor antagonists, and nonpharmacologic therapies such as nasal irrigation.

Antihistamine drugs can have undesirable side-effects, most notably drowsiness. First generation antihistamine drugs such as diphenhydramine cause drowsiness, but not second- and third-generation antihistamines such as cetirizine and loratadine.

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 (Rhinitis medicamentosa).

For nocturnal symptoms, intranasal corticosteroids can be combined with nightly oxymetazoline, an adrenergic alpha-agonist, without risk of rhinitis medicamentosa.

Desensitization
More severe cases of allergic rhinitis not responding to medication may benefit from allergen immunotherapy (allergy shots).

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.

Epidemiology
In Western countries between 10–25% of people annually are affected by allergic rhinitis.