St. Louis, MO Pollen Levels Today

Situated in the humid continental climate of the Mississippi and Missouri River confluence, St. Louis consistently ranks among the more challenging U.S. cities for seasonal allergies. The region's long growing season, high summer humidity, and riverine geography create conditions that sustain airborne allergens nearly year-round.

Tree pollen kicks off the allergy calendar in late February and peaks from March through May, with oak, maple, cedar, elm, sycamore, hickory, and cottonwood serving as the most prolific local offenders. As tree counts taper, grass pollen takes over from May into July, dominated by Kentucky bluegrass, timothy, orchard grass, and Bermuda.

By mid-August, weed season ramps up and runs through the first hard frost in October or November, with ragweed as the primary culprit alongside lamb's quarters, pigweed, and plantain. The overlap between lingering grasses and early ragweed in August often intensifies symptoms for sensitized residents.

Beyond pollen, St. Louis's humidity fuels persistent outdoor and indoor mold, particularly Alternaria and Cladosporium, while dust mites thrive in muggy summers and the city's ozone and particulate pollution can compound respiratory irritation.

Overall, St. Louis's allergy profile is defined by extended seasons, heavy ragweed exposure, and mold-amplifying humidity.