| 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 |
