Pollen levels are high right now because of a combination of seasonal timing, warming temperatures that have stretched pollen seasons longer than they used to be, and weather patterns that concentrate pollen in the air. Depending on where you live and the time of year, you may be dealing with tree, grass, or weed pollen, or a combination of all three. The short answer: pollen seasons in North America have grown roughly 20 days longer and pollen concentrations have increased by about 21% since 1990, so “high pollen” days are more frequent than they were a generation ago.
Which Pollen Is Peaking Right Now
Pollen seasons follow a predictable calendar, though exact timing shifts by region. Tree pollen dominates from March through May. Grass pollen picks up in late spring and runs through early summer. Ragweed and other weed pollens take over from August through November. During the transitions between these windows, multiple pollen types overlap, which is why late spring and early fall tend to feel the worst.
If you’re reading this in spring, tree pollen is likely the primary culprit. Cities like Wichita, Oklahoma City, and Tulsa consistently rank among the worst in the country for tree and grass pollen, according to the Asthma and Allergy Foundation of America’s 2025 rankings. New Orleans and Memphis round out the top five, driven by high grass and weed pollen. These cities combine warm climates, long growing seasons, and large numbers of pollen-producing plants.
Climate Change Has Made It Worse
This isn’t just your imagination. A large-scale study published in the Proceedings of the National Academy of Sciences tracked pollen data across North America from 1990 to 2018 and found that pollen seasons now start about 20 days earlier than they did three decades ago. The total amount of pollen released each year has jumped by roughly 21%, with spring pollen (February through May) increasing by a nearly identical margin.
Warmer winters mean plants begin producing pollen sooner. Longer frost-free periods give them more time to do it. Higher carbon dioxide levels also fuel plant growth, which translates directly into more pollen per plant. These aren’t subtle shifts. If you feel like your allergies have gotten worse over the years, the data supports that experience.
Your Body Gets More Reactive Over the Season
There’s a biological reason why your allergies may feel worse in the middle of the season even if pollen counts haven’t changed much. It’s called the priming effect. As your immune system encounters pollen day after day, it ramps up its response. Your body produces more of the antibodies (IgE) that trigger allergy symptoms, making your airways and nasal passages increasingly sensitive to the same amount of pollen.
This means a pollen count that barely bothered you in early March could leave you miserable by late April. The effect is reversible: a few pollen-free days can reset the sensitivity. That’s why a stretch of rain often brings temporary relief, not just because it washes pollen out of the air, but because the break in exposure lets your immune system dial back its overreaction.
Time of Day Matters More Than You Think
Pollen counts aren’t constant throughout the day. Research from the American College of Allergy, Asthma & Immunology found that pollen levels are lowest between 4:00 a.m. and noon, then climb through the afternoon, peaking between 2:00 and 9:00 p.m. This runs counter to what many people assume. Morning may actually be your best window for outdoor activity during allergy season, not the worst.
Warm, dry, windy afternoons are the classic high-pollen scenario. Wind carries pollen farther, and dry conditions keep grains airborne longer. On calm, humid mornings, much of the pollen stays closer to the ground or hasn’t yet been released from the plants.
How Thunderstorms Can Make Pollen Dangerous
Rain usually helps clear pollen from the air, but thunderstorms are a different story. High humidity and the mechanical forces inside a storm can cause pollen grains to absorb water and burst open, releasing tiny fragments called sub-pollen particles. Whole pollen grains are large enough that they mostly get trapped in your nose and upper airways. These fragments are small enough to travel deep into your lungs, which is why thunderstorm asthma is a real phenomenon. People who normally just get a runny nose from pollen can experience wheezing and serious breathing difficulty during or right after a storm.
The exact mechanisms aren’t fully understood, but researchers believe wind gusts, lightning, and moisture all play a role in rupturing the grains. If you notice your symptoms suddenly worsen after a thunderstorm, this is likely why.
What the Pollen Count Numbers Mean
When your weather app shows a pollen count, it’s measured in grains per cubic meter of air. The thresholds vary by pollen type because some species produce far more pollen than others. For tree pollen, “high” starts at 90 grains per cubic meter and “very high” kicks in above 1,500. Grass pollen triggers “high” at just 20 grains per cubic meter, with “very high” above 200. Weed pollen hits “high” at 50 grains and “very high” above 500.
These categories were developed by the National Allergy Bureau based on years of data correlating pollen concentrations with symptom severity. If your area is reporting “high” or “very high” for any category, most people with sensitivities to that pollen type will notice symptoms.
Reducing Your Exposure at Home
HEPA filters are the gold standard for removing pollen indoors. They capture at least 99.97% of particles as small as 0.3 microns, and pollen grains are significantly larger than that, so HEPA filtration is extremely effective. A standalone air purifier with a true HEPA filter in your bedroom can make a noticeable difference in sleep quality during peak season.
For your central HVAC system, look for filters with higher MERV ratings. MERV measures how well a filter captures particles between 0.3 and 10 microns. The higher the rating, the more pollen gets trapped before circulating through your home. Keeping windows closed during afternoon and evening hours, when pollen peaks, is one of the simplest steps you can take. Changing clothes and showering after spending time outdoors prevents pollen from settling into furniture and bedding, where it continues to trigger symptoms long after you’ve come inside.
Why Some Cities Are Worse Than Others
Geography, climate, and urban planning all influence local pollen levels. Cities in the South and Central Plains tend to have longer growing seasons, more diverse plant species producing pollen, and warm winds that carry pollen across wide areas. Wichita tops the 2025 allergy rankings largely because of its worse-than-average tree and grass pollen combined with high allergy medication use, suggesting residents are struggling more than the national average.
There’s been popular discussion about “botanical sexism,” the idea that cities have made allergies worse by planting male trees (which produce pollen) instead of female trees (which don’t). A USDA Forest Service study in New York City found this effect is real but small, accounting for only a few percent of total allergenic pollen exposure. The biggest pollen producers in urban areas tend to be naturally regenerating species that weren’t deliberately planted at all, like white mulberry trees that sprout in vacant lots and along fence lines. That said, in regions with more wind-pollinated species, choosing female trees for new plantings could modestly reduce local pollen levels over time.