While many people associate pollen with the spring months, a significant amount of airborne pollen is present during autumn. This causes what is commonly known as hay fever or seasonal allergic rhinitis for millions of people. The symptoms of fall allergies are similar to those experienced in the spring, including sneezing, congestion, and itchy, watery eyes. The fall season marks a distinct shift in the type of plant releasing pollen, creating a second major peak for symptoms.
The Primary Source of Fall Pollen
The primary biological sources of pollen shift dramatically once summer ends, moving away from the trees and grasses that dominate the earlier seasons. The arrival of autumn signals the season of the weeds, which are the main culprits behind fall pollen allergies.
The single largest source of allergenic pollen in the fall is the ragweed plant. Though it only lives for one season, a single ragweed plant can produce up to a billion grains of lightweight pollen. This light pollen is easily picked up by the wind and can travel for hundreds of miles, affecting people far from where the plant grows. Ragweed is particularly prevalent across the Eastern and Midwest regions of the United States.
While ragweed is the dominant allergen, other weeds also release pollen during the autumn months. Depending on the specific geographic area, plants such as sagebrush, pigweed, tumbleweed, and Russian thistle can contribute to the overall weed pollen count.
The Fall Pollen Timeline
The fall pollen season is tied to the transition from summer weather patterns. Weed pollen, particularly from ragweed, typically begins to appear in the air starting in late summer, often around mid-to-late August. This initial appearance quickly ramps up as the days shorten.
The season reaches its peak intensity during the first half of September in many areas, creating the highest concentrations of airborne pollen. The season’s end is not determined by a calendar date but by a specific meteorological event: the first hard frost. A hard frost occurs when temperatures drop consistently below freezing, which destroys the ragweed plant and eliminates the airborne allergen. Depending on the regional climate, this can happen anywhere from late October to well into November, and in warmer regions, the season can persist even longer.
How Weather Influences Fall Pollen Counts
Daily weather conditions determine how much pollen is in the air. High winds are effective at scattering pollen widely, lifting ragweed grains and carrying them over great distances. Dry, windy conditions on a warm day can lead to a surge in pollen counts, exacerbating symptoms for allergy sufferers.
Rainfall provides temporary relief by washing the airborne pollen out of the atmosphere. While a rainy day lowers the pollen count, levels can quickly soar again once the rain stops and the ground begins to dry. Temperature and time of day also influence the concentration of pollen.
Pollen levels tend to be highest during the morning hours, often peaking around midday. Warm, dry mornings allow for efficient pollen release and dispersion. Sensitive individuals can minimize their exposure by avoiding outdoor activity during these peak times.