Hay fever

Hay fever is caused by pollens of specific seasonal plants in people who are allergic to these substances. It is characterised by sneezing, runny nose and itching eyes. This seasonal allergic rhinitis is commonly known as 'hay fever', because it is most prevalent during haying season. It is particularly prevalent from late May to the end of June (in the Northern Hemisphere).

Causes
As noted above, hay fever involves an allergic reaction to 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-pollinated plants are the predominant culprits. 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 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 most predominant in Mediterranean regions.
 * Grasses (Family Poaceae): especially ryegrass (Lolium sp.) and Timothy-grass (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.

The time of year at which hay fever symptoms manifest themselves varies greatly depending on the types of pollen to which an allergic reaction is produced. The pollen count, in general, is highest from mid-spring to early summer. As most pollens are produced at fixed periods in the year, a long-term hay fever sufferer may also be able to anticipate when the symptoms are most likely to begin and end, although this may be complicated by an allergy to dust particles.

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

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

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

Symptoms
The effect of hay fever can vary greatly: some people may only be mildly afflicted, whereas others may suffer greatly. Common symptoms include:
 * coughing
 * headache
 * itching nose, mouth, eyes, throat, skin, or any area exposed to the allergen.
 * runny nose (and occasionally nosebleeds)
 * impaired smell (and thus sensitivity to flavours)
 * sneezing
 * stuffy nose (nasal congestion)
 * watering eyes and/or plugged up ear canals.
 * sore throat
 * wheezing
 * cross-reactivity allergy to some fruits
 * conjunctivitis
 * fever
 * fatigue
 * flushing

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 diet changes.

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 some individuals who cannot undergo skin testing (as determined by the doctor), the RAST blood test may 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 or apples. This occurs because of similarities in the proteins of the pollen and the food. There are many cross-reacting substances.

Prevention
Avoiding exposure to pollen is the best way to decrease allergic symptoms.
 * Remain indoors in the morning and evening when outdoor pollen levels are highest.
 * Wear face masks designed to filter out pollen if you must be outdoors.
 * Keep windows closed and use the air conditioner if possible in the house and car.
 * Do not dry clothes outdoors.
 * Avoid unnecessary exposure to other environmental irritants such as insect sprays, tobacco smoke, air pollution, and fresh tar or paint.
 * Avoid mowing the grass or doing other yard work, if possible. Avoid fields and large areas of grassland.
 * Regular hand- and face-washing removes pollen from areas where it is likely to enter the nose.
 * A small amount of petroleum jelly around the eyes and nostrils will stop some pollen from entering the areas that cause a reaction
 * Avoid bicycling or walking - instead use a method of confined transportation such as a car.
 * Wear sunglasses, which reduce the amount of pollen entering the eyes.

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:


 * Fast-acting strong antihistamines such as drugs including chlorphenamine which relieve the symptoms after a hayfever "attack".
 * 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. Azelastine (Astelin®) is the only antihistamine 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).
 * New leukotriene receptor antagonists, such as montelukast (Singulair) and zafirlukast (Accolate) have proven very effective in dealing with allergic rhinitis, without the common side-effects of the first-generation antihistamines, such as drowsiness. These medicines are also long-acting, and are recommended to be taken once-daily.
 * Corticosteroid nasal sprays are effective and somewhat safe, and may be effective without oral antihistamines. These medications include fluticasone (Flonase/Flixonase), budesonide (Rhinocort), flunisolide (Syntaris), mometasone (Nasonex), triamcinolone (Nasacort) and beclomethasone (Beconase®).
 * 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).
 * Cromolyn sodium (or cromoglycate) is a drug that stabilizes mast cells and prevent their degranulation and subsequent release of histamine. It is available as a nasal spray (Nasalcrom) for treating hay fever. Eye drop versions of cromolyn sodium (Crolom) 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. These tend to be offered as a last resort as the therapy is more expensive at first, although patients may save money on medications and doctor visits in the long run. They may also increase the risk of triggering a secondary allergic reaction such as an asthma attack.

A large number of over-the-counter treatments are sold without FDA approval but are known for their positive effects, including herbs like eyebright (Euphrasia officinalis), nettle (Urtica dioica), and bayberry (Myrica cerifera), which have not been shown to reduce the symptoms of nasal-pharynx congestion. In addition, feverfew (Tanacetum parthenium) and turmeric (Curcuma longa) has been shown to inhibit phospholipase A2, the enzyme which releases the inflammatory precursor arachidonic acid from the bi-layer membrane of mast cells (the main cells which respond to respiratory allergens and lead to inflammation) but this is only in test tubes and it is not established as antiinflammatory in humans.

Allergen immunotherapy
Allergen immunotherapy is commonly used in patients suffering from allergic rhinitis, allergic asthma, or life threatening stinging insect allergy. This type of therapy has been found to potentially alter the course of all three of the above disorders. Allergen immunotherapy provides long-term relief of the symptoms associated with rhinitis and asthma.

Honey
Eating locally produced unfiltered honey is believed by many to be a treatment for hayfever, supposedly by introducing manageable amounts of pollen to the body. Clinical studies have not provided any evidence for this belief.

Homeopathy
It has been claimed that homeopathy provides relief free of side-effects. However, this is strongly disputed by the medical profession on the grounds that there is no valid evidence to support this claim. The list of suggested medication includes
 * arundo mauritanica
 * galphimia glauca
 * luffa

Acupuncture
Therapeutic efficacy of complementary-alternative treatments for rhinitis and asthma is not supported by currently available evidence.

Nevertheless, there have been some attempts with controlled trials to show that acupuncture is more effective than antihistamine drugs in treatment of hay fever. Complementary-alternative medicines such as acupuncture are extensively offered in the treatment of allergic rhinitis by non-physicians but evidence-based recommendations are lacking. The methodology of clinical trials with complementary-alternative medicine is frequently inadequate. Meta-analyses provides no clear evidence for the efficacy of acupuncture in rhinitis (or asthma). It is not possible to provide evidence-based recommendations for acupuncture or homeopathy in the treatment of allergic rhinitis.

Expectations
Most symptoms of allergic rhinitis can be readily treated.

In some cases (particularly in 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

 * drowsiness and other side effects of antihistamines
 * side-effects of other medications (see the specific medication)
 * asthma
 * sinusitis
 * nasal polyps
 * disruption of lifestyle (usually not too severe)

A case-control study found "symptomatic allergic rhinitis and rhinitis medication use are associated with a significantly increased risk of unexpectedly dropping a grade in summer examinations".