Seasonal allergies are allergies which occur at certain times of the year from a sensitivity to pollens from trees,
grasses, or weeds.  The pollen from these plants is very small and light
and can be carried by the wind hundreds of
, and easily enters the nasal passages and airways.  Affected individuals will develop allergy or asthma
symptoms when the  pollens come into contact with the mucus membranes of the nose, throat, lungs or eyes.     

Roughly, the different pollen seasons run as follow:

Northern USA
Trees:  February/March to May
May to late June/early July time frame ; some grasses may pollinate in late summer/early fall as well
Weeds: August to November

Southern USA  (to include California, New Mexico, Texas, Mississippi, Georgia, Florida)
Trees:  February to June
Grasses: February to September
Weeds: August to November; may start as early as July in Florida

Common trees causing allergies in the USA include Oak, Birch, Beech, Maple, Elm, Sycamore, Hackberry,
Cottonwood, Pecan, Olive, and Cedar trees. Common grasses include Johnson, Rye,Orchard, and T
grasses in the northern USA and Bahia and Bermuda grasses in the South.  Common weeds causing allergies
include Ragweed, Cocklebur, Pigweed, and Sagebrush.  In England, the major allergens include Birch in the
Spring (March to May) and Rye grass in the summer (June-August).

Updated 24 June 2013
What are Seasonal Allergies?

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