Allergic rhinitis, known as hay fever, is caused by pollens of specific seasonal plants, airborne chemicals and dust particles 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). However it is possible to suffer from hay fever throughout the year.
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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 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 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 (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.
The two categories of allergic rhinitis include:
seasonal - occurs particularly during pollen seasons. Seasonal allergic rhinitis does not usually develop until after 6 years of age.
perennial - occurs throughout the year. This type of allergic rhinitis is commonly seen in younger children.[1]
