Seasonal allergies, formally known as allergic rhinitis, are an immune system response to harmless airborne particles, primarily from plants. When inhaled, the body mistakenly identifies these microscopic substances as a threat and releases chemicals like histamine. This reaction results in familiar symptoms such as sneezing, watery eyes, and nasal congestion. The “peak allergy season” refers to the time of year when the concentration of airborne allergens is highest, leading to maximum symptom severity for sufferers.
The Primary Allergy Seasons and Their Triggers
The calendar year features a predictable succession of three pollen seasons, each triggered by a different type of plant life. Tree pollen initiates the cycle, typically starting in late winter or early spring, generally from February through May. Common wind-pollinated trees that cause symptoms include oak, birch, maple, and cedar, which release their powdery grains into the air before their leaves fully emerge.
Following the tree pollen season, grass pollen takes over as the dominant allergen, generally spanning from late spring into mid-summer, specifically May through July. Grasses like Bermuda, Timothy, and Kentucky bluegrass produce this allergen. This pollen can be easily stirred up by activities such as lawn maintenance or walking through a field, triggering symptoms for many people.
The final major outdoor season is driven by weed pollen, beginning in late summer and lasting until the first hard frost, typically from August through November. Ragweed is the most common culprit during this period, with a single plant capable of producing vast amounts of pollen grains that can travel for hundreds of miles. Outdoor mold spores also contribute to this peak, thriving in the damp conditions created by decaying leaves and soil.
Regional Differences in Timing
The precise timing of these seasonal peaks is dependent on local climate and geography, meaning the peak is not uniform across all regions. In the Southern United States, milder winters allow plants to begin pollination much earlier, often as early as January or February. This results in an extended allergy season, sometimes causing nearly year-round exposure for residents.
In contrast, Northern climates, such as the Northeast and Midwest, experience a shorter, more condensed season. The colder winters delay the initial plant growth, so the allergy season does not typically begin until March or April. When the warm weather finally arrives, the rapid onset of growth can lead to a sudden, intense burst of pollen, resulting in a severe, albeit shorter, peak period.
Other geographical factors also alter the local peak timing and allergen concentration. Higher humidity, which is common in coastal or low-lying areas, encourages the growth of mold spores, making them a more persistent problem throughout the summer and fall. Similarly, elevation can influence timing, as mountainous regions often have a later and shorter pollen season compared to lower-lying valleys.
Understanding Pollen Counts
The actual “peak” of allergy season is defined by the pollen count, which is a quantified measurement of airborne allergen concentration. This count is determined by using specialized instruments, such as a Rotorod or Burkard sampler, which draw in a known volume of air over a 24-hour period. These devices collect the particles onto a sticky surface for analysis under a microscope.
The final count is reported as the number of pollen grains identified per cubic meter of air. This raw number is then translated into a simple risk scale for public consumption, categorized as Low, Moderate, High, or Very High. A “peak” allergy period corresponds to the High or Very High category, which is defined by specific numerical thresholds for each allergen type.
For instance, a tree pollen count above 90 grains per cubic meter is considered High, while a grass pollen count above 20 grains per cubic meter can reach the High range. Tracking these daily counts is a practical tool used by meteorologists and health organizations to determine when the air quality is most likely to trigger symptoms in sensitive individuals.