Allergy Shots in Illinois: What to Know

Short and giant ragweed thrive across Illinois's vast corn-and-soybean belt, where disturbed field margins generate some of the highest ragweed pollen counts in the Midwest from August through September.

Illinois's cornbelt produces one of the nation's largest ragweed loads

Red oak (Quercus rubra) and bur oak (Q. macrocarpa) dominate Illinois forests and urban street plantings. Spring pollen loads peak statewide in April and May, with Chicago's mature tree canopy intensifying counts in the metro area.

Primary spring tree allergen across the state

Silver maple and box elder are among the first trees to pollinate in Illinois, releasing moderate pollen loads from March through April along river corridors and residential streets statewide.

Early-spring tree allergen prevalent in river valleys

Kentucky bluegrass and timothy grass blanket Illinois lawns, parks, and pastures. Suburban communities in DuPage and Lake counties report especially heavy grass pollen from May through June.

Dominant grass allergen; suburban lawns amplify exposure

Alternaria alternata peaks alongside ragweed in late summer, thriving on decomposing corn and soybean residues across central and southern Illinois. Counts remain elevated from spring through fall.

Agricultural residues drive severe Alternaria loads statewide

Cladosporium spores peak during Illinois's hot, humid summers and persist from spring into fall. Lake Michigan humidity along the lakefront and river valleys sustain elevated counts through August.

Sustained by Midwest summer humidity