Major causes of allergic rhinitis according to timing of symptoms

Season	Antigens	Examples
Early spring	Tree pollens	Oaks, maples, elms, birches, etc (trees without showy flowers)
Spring/summer	Grass pollens	Ryegrass, bluegrass, Bermuda grass
Late summer	Weed pollens	Ragweed
Throughout the growing season	Fungi
Throughout the year	Household allergens	House dust mites, cockroaches, animal dander, molds
Occupational		Seed dusts, woods, furs, latex, flour, psyllium, and many others

Adapted from Naclerio R, Solomon W, JAMA 1997; 278:1842.

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