Seasonal allergies (allergic rhinitis) are an immune system overreaction to harmless airborne particles, primarily pollen. When inhaled, these microscopic grains trigger symptoms like sneezing, nasal congestion, and itchy eyes. The yearly onset of symptoms is highly variable, depending on the specific plant releasing the allergen and local environmental conditions. Pinpointing the exact start date is complex because pollen release is tied to weather, not the calendar. Understanding the general timeline and the factors that modify it helps in preparing for the allergy season.
The Typical Allergy Season Calendar
The allergy year is segmented into three distinct phases, each dominated by a different type of plant pollen.
Tree pollen is the first to arrive, signaling the start of the spring allergy season from late February or early March through May. Common culprits include oak, birch, maple, and cedar, which release their fine, powdery allergens into the warming air.
As the tree pollen season subsides, grass pollen takes over, typically dominating the late spring and summer months from May through July. Grasses such as Timothy, Kentucky Bluegrass, and Bermuda are major contributors. Those sensitive to both tree and grass pollens may experience prolonged discomfort stretching into the summer.
The third phase is driven by weed pollen, most notably ragweed, which emerges in late summer and continues until the first hard frost. Ragweed begins releasing its potent pollen around mid-August. This fall allergy season can extend as late as November or early December in regions that experience milder autumns.
Environmental Factors That Shift the Start Date
While the calendar provides a general framework, the actual start date of the pollen season is dictated by specific environmental conditions. Plant life cycles are responsive to accumulated heat, meaning warmer winters and early spring temperatures cause plants to pollinate sooner. This phenomenon can push the onset of tree pollen season forward by several weeks, an effect sometimes described as “pollen creep.”
Climate change contributes to this variability by increasing average global temperatures, leading to a longer growing and pollination season overall. The season starts earlier, and plants like ragweed may produce more pollen for a longer duration due to elevated carbon dioxide levels. This shift means the period between the first pollen release in spring and the final weed pollen in fall is continually expanding.
Geographical location and latitude also play a role in determining the initial start date. Regions in the Southern United States, with warmer climates, may see the first tree pollens as early as January or February. Conversely, Northern states and Canada typically experience a delay, with their allergy season starting later in March or April.
Identifying the Start of Allergy Season in Your Area
Given the significant variability influenced by weather and latitude, the most effective way to identify the current start of allergy season is by monitoring local pollen count reports. These reports measure the concentration of airborne pollen grains per cubic meter of air, providing a real-time assessment of the allergen threat. Many local weather forecasts, national allergy websites, and mobile applications provide these daily counts.
Pollen counts are generally categorized using a simple scale, such as low, moderate, high, and severe. A high count indicates that most people sensitive to that specific pollen type will experience symptoms, signaling the active start of that season. Checking forecasts that break down the count by specific allergen—tree, grass, or weed—allows for targeted preparation.