North America

Stay away from these plant species if you are in America: The main tree pollens present in North America, which are responsible for seasonal allergic symptoms, include the alder, oak, western red cedar, maple, elm , birch , ash , hickory , poplar , American sycamore, cypress , and walnut. The main grass pollens include timothy grass , Bermuda couch grass , orchard grass, sweet vernal grass , red top grass and different types of blue grasses.

Weed pollens include the dandelion, goldenrod, nettle and sage but it is the ragweed pollen that causes the most problems in North America. Ragweed (Ambrosia artemisiifolia) pollen may travel as far as 400 miles and as high as 2 miles in the air.