Aeroallergen - Pollens

Pollens

Aeroallergens include the pollens of specific seasonal plants is commonly known as "hay fever", because it is most prevalent during haying season, from late May to the end of June in the Northern Hemisphere; but it is possible to suffer from hay fever throughout the year.

The pollen which causes hay fever varies 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 plant pollen commonly responsible for hay fever include:

• Trees: such as birch (Betula), alder (Alnus), cedar (Cedrus), 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)

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.