Fall Allergy Forecast: These Allergens Will Be Worst In IL

Illinois residents with seasonal allergies may want to keep the tissues handy as fall approaches.

Weed pollen is expected to be the biggest allergy concern across much of the country this fall, while grass pollen could remain troublesome in parts of the East and Midwest, according to AccuWeather's 2026 fall allergy forecast.

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The meteorology company, based on the campus of Penn State University, says the East will have the best chance of lingering grass pollen trouble spots, especially where warm nights and enough moisture keep grass growing. The highest grass pollen levels are predicted across the mid-Atlantic and across the Midwest, including areas in and around New York City, Philadelphia, Detroit and Chicago.

For Chicago and much of northern Illinois, the forecast points to a potentially rough stretch for allergy sufferers as summer gives way to fall. AccuWeather's map places the Chicago area in one of the zones expected to see high grass pollen levels into September, while weed pollen is also forecast to run above average across Illinois during the August-through-October period.

The combination could mean overlapping allergy triggers for some residents, particularly during warm, dry stretches that allow grasses and weeds to keep producing pollen. AccuWeather notes that rain can temporarily knock pollen out of the air, but levels can rebound in the days afterward as weeds take advantage of the added moisture and resume growth.

Fall allergy season is already ramping up, with warm and wet weather helping pollen levels climb in parts of the country, especially across the eastern half of the United States, AccuWeather said. Grass and weed pollen typically cause the most trouble late in the summer and early in the fall.

Grass pollen tends to ease during August and early September, but it can remain high where there is enough moisture and overnight temperatures stay warm. AccuWeather senior meteorologist Alan Reppert said.

Drier weather should limit grass growth across much of the West outside irrigated areas, while stretches of dry weather are expected to keep grass pollen below typical levels in many parts of the Southeast.

Weed pollen is expected to be a more widespread problem and could linger into October. The highest levels are forecast across the Southeast and southern Rockies, including areas around Raleigh, Nashville, Atlanta, Little Rock, Denver, Salt Lake City and Albuquerque.

Dry weather across the northern half of the country could suppress weed growth and produce a less severe season in some areas. Still, warmth across much of the United States could produce occasional spikes in pollen levels, according to AccuWeather.

Rain may temporarily clear some pollen from the air, but it can also fuel new weed growth and cause pollen levels to rise again in the days that follow.

People with fall allergies can reduce exposure by keeping windows closed on high-pollen days, using air conditioning or an indoor air purifier when possible, checking pollen levels before spending extended time outdoors, changing clothes after being outside, and showering before bed, AccuWeather said.

People with asthma or more severe allergy symptoms should follow their health care provider's guidance, particularly when pollen levels are high or symptoms interfere with sleep, work or school.