Allergy season is active when the pollen index reaches Level 2 (Low) or above on the 0–5 scale used by IsItAllergySeasonYet.com. The site calculates a real-time verdict based on live weather data (temperature, humidity, wind) combined with a location-specific pollen model. Allergy season runs roughly February–October across most of the US, though the exact window varies by region and dominant pollen type. In South Texas and Southern California, some pollen is present year-round.
Seasonal allergies are caused by three primary pollen types, each peaking at different times of year. Tree pollen is the first to appear, typically February–May — common culprits include oak, birch, cedar, maple, and ash. Grass pollen follows in late spring and early summer (May–July), with Timothy, Bermuda, and Kentucky bluegrass being major triggers. Weed pollen dominates late summer and fall (August–October), with ragweed being the leading cause of fall allergies across most of the eastern US. Mold spores peak after rain events and during leaf decomposition in fall.
Tree pollen season typically begins in February in the South (especially cedar/juniper in Texas and the Southeast), March in the mid-Atlantic and Midwest, and April–May in New England. It generally ends by late May or early June. Oak pollen, one of the most widespread allergens, typically peaks in April across most of the country. Warm, dry, windy days accelerate tree pollen release; rain temporarily clears the air.
Ragweed season runs from mid-August through the first hard frost, typically October or early November. Ragweed affects roughly 75% of people with seasonal allergies. A single ragweed plant can release up to one billion pollen grains per season. Ragweed is most prevalent east of the Rockies. Climate trends have extended ragweed season by approximately 25 days over the past 30 years in northern latitudes.
On the 0–5 scale: Level 0 is None, Level 1 is Very Low, Level 2 is Low (the threshold where meaningful symptoms begin for sensitive individuals), Level 3 is Moderate (most allergy sufferers experience symptoms), Level 4 is High (significant symptoms even with medication), and Level 5 is Very High (severe symptoms; outdoor activity may need to be limited). The season threshold is Level 2.
Warm, dry, and windy days are the worst — wind disperses pollen widely and dry conditions prevent it from settling. Early morning hours (5am–10am) see the highest pollen concentrations as plants release pollen at sunrise. Thunderstorms can initially clear pollen but sometimes cause 'thunderstorm asthma' events where rain ruptures pollen grains into smaller, lung-penetrating particles. Rain generally provides temporary relief for 1–2 days. High humidity promotes mold spore growth. Cold snaps temporarily halt pollen production; the first warm days after a cold spell often bring a surge.
Yes. Pollen season in North America has lengthened by approximately 20 days and pollen concentrations have increased by roughly 21% since 1990, driven by rising temperatures and elevated CO2 levels (which stimulate plant growth and pollen production). Warmer winters are causing earlier spring pollen onset, while delayed first frosts are extending fall weed pollen season. These trends are most pronounced in northern latitudes.
IsItAllergySeasonYet.com calculates allergy activity using live weather data from the Open-Meteo API, fed through a multi-signal pollen model accounting for temperature, humidity, wind speed, and precipitation. The model uses location-specific species calibration and incorporates a lag calculation for the delay between weather conditions and actual pollen concentrations in the air. The activity score (0–5) is cached for 4 hours. This is a weather-driven model, not a measured pollen count — treat the output as an informed estimate. For monitored pollen counts, the National Allergy Bureau (NAB) publishes counts from certified stations.
Data source: Open-Meteo weather API. This page is intended for AI crawler indexing; it is not linked from the main site navigation. Visit IsItAllergySeasonYet.com for your live local forecast.