Allergy season in the United States isn’t a single season. It runs from early February through the first hard frost in fall, with different allergens peaking at different times. Depending on where you live and what you’re allergic to, your personal allergy season could last a few weeks or stretch across most of the year.
Spring: Tree Pollen (February Through May)
Spring is when most people first notice allergy symptoms. Tree pollen season runs from February through the end of May, starting earlier in southern states and arriving later in the north. Juniper, maple, and elm trees are often the first to release pollen, followed by pines, oaks, hickory, and ash. If you start sneezing in late winter before anything looks green, early-blooming trees like juniper are likely the cause.
In the Deep South and Southwest, tree pollen can appear as early as January. In northern states like Minnesota or Wisconsin, it may not ramp up until March or April. This staggered start means “allergy season” can begin two full months earlier for someone in Texas than for someone in Michigan.
Late Spring and Summer: Grass Pollen (April Through June)
Grass pollen picks up where tree pollen starts to taper off. It’s most common from April through early June, though in warmer parts of the country (California, Texas, and much of the South) grass pollen can linger year-round. Common culprits include Bermuda, Timothy, Kentucky bluegrass, rye, and fescue.
For many people, the overlap of tree and grass pollen in April and May creates the worst stretch of the entire year. If your symptoms peak in late spring, grass pollen is a likely trigger, especially if you notice them worsening after mowing the lawn or spending time in open fields.
Fall: Ragweed and Mold (August Through First Frost)
Fall allergy season is dominated by ragweed. It starts around August and lasts six to ten weeks, peaking in mid-September and continuing through October in most of the country. Symptoms persist until the first hard frost kills the plants. A single ragweed plant can release a billion grains of pollen in a season, and that pollen can travel hundreds of miles on the wind, so you don’t need ragweed in your own yard to be affected.
Mold spores also spike in fall. Dying and decomposing plants create concentrations of mold in the air, and spore counts can soar one to four days after a rainstorm. If your symptoms get worse on damp fall days or right after rain, outdoor mold is worth considering as a trigger alongside ragweed.
Winter: Indoor Allergens Take Over
Outdoor pollen drops to near zero once freezing temperatures arrive, but that doesn’t mean allergy symptoms disappear. Winter brings a different set of triggers, all of them indoors. Sealed windows, dry heating systems, and hours spent inside create the perfect conditions for allergen buildup.
Dust mites thrive in warm, humid spots like bedding, upholstered furniture, and carpets. Pet dander becomes a bigger problem when you and your animals are sharing tightly sealed indoor spaces for months. Mold can grow in bathrooms, basements, and anywhere indoor humidity stays high with limited ventilation. Heating systems also dry out the mucous membranes in your nose and throat, making them more vulnerable to irritation from any of these triggers. If your “cold” seems to last all winter without a fever, indoor allergens are a common explanation.
How Location Changes Your Timeline
Geography is one of the biggest factors in how long your allergy season lasts. Research tracking pollen-counting stations from east Texas to central Canada found that pollen season has been lengthening more at higher latitudes, by 13 to 27 extra days north of roughly the latitude of Minneapolis. At the southernmost station in Georgetown, Texas, the season length barely changed at all, largely because it was already long to begin with.
In practical terms, this means northern states now have allergy seasons that start earlier and end later than they did a generation ago. Southern states have always dealt with extended pollen exposure, with grass pollen circulating nearly year-round in many areas. Coastal and humid regions also contend with higher mold spore counts throughout more of the year.
Allergies vs. a Cold
Seasonal allergies and the common cold share a lot of symptoms: sneezing, congestion, runny nose, and fatigue. The easiest way to tell them apart is duration. A cold typically lasts 3 to 10 days. Seasonal allergies last several weeks, often the entire duration of whatever pollen is in the air. Allergies also tend to produce clear, watery nasal discharge and itchy eyes, while colds are more likely to cause thick or discolored mucus, sore throat, and sometimes a low fever. If your symptoms follow a predictable calendar pattern year after year, allergies are the more likely cause.
Reducing Your Exposure
Pollen levels follow a daily pattern that might surprise you. Research measuring airborne pollen found that concentrations are lowest between 4 a.m. and noon, then climb gradually through the afternoon, reaching their peak between 2 p.m. and 9 p.m. If you want to exercise or spend time outside, morning is your best window.
Beyond timing, a few habits make a noticeable difference. Showering and changing clothes after spending time outdoors keeps pollen from following you inside. Running the air conditioner with a clean filter, rather than opening windows, helps keep indoor air pollen-free during peak months. Checking your local pollen forecast before planning outdoor activities gives you a heads-up on especially bad days. On high-count days, drying clothes in a dryer instead of on a line prevents them from collecting pollen.
For indoor allergens in winter, improving ventilation even briefly, washing bedding in hot water weekly, and using a dehumidifier in damp areas can reduce dust mite and mold exposure significantly.