Spring allergies are caused by the immune system’s overreaction to wind-borne pollen grains from trees, grasses, and weeds. Determining the duration of this period is complex, as it is highly variable depending on local climate patterns and geographic area. The overall length of the season is defined by the full cycle of plant pollination, from the first tree pollen release to the peak of grass pollen activity.
Understanding the Standard Spring Allergy Timeline
The typical spring allergy timeline follows a predictable, sequential release of pollen types, which dictates the total duration of the season. The season generally begins in late winter or early spring, as soon as temperatures rise consistently above freezing. This initial phase, starting as early as February in some areas, is dominated by the release of tree pollen from species like oak, maple, and birch.
Tree pollen often continues through late May or early June. As tree pollination subsides, the season transitions into its second phase, dominated by grass pollen, which typically begins major production in April or May.
The peak of the spring allergy season generally occurs around late April and May, when the end of tree pollen overlaps with the beginning of grass pollen. This combination leads to the highest concentration of airborne allergens. The spring season concludes for many people in early summer, around June, before the emergence of weed pollens, like ragweed, begins.
How Geographic Location Changes the Season Length
Geographic location strongly modifies the spring allergy timeline because the season’s start is tied directly to local temperatures. The Southern U.S. often experiences the earliest start, with tree pollen appearing as early as January or February due to milder winters, resulting in a significantly longer duration compared to northern regions.
In the Northeast and Midwest, colder, longer winters delay the onset until March or April. Although the start is later, the season can feel more intense because warmer temperatures arrive quickly, causing multiple tree and grass species to release pollen almost simultaneously. The West Coast and Southwest can also have extended seasons due to diverse, persistent flora.
Elevation also plays a significant role. Mountainous regions typically have a delayed and shorter season due to sustained lower temperatures, and pollen counts are often lower at higher altitudes, offering a reprieve for some allergy sufferers.
Environmental Factors That Extend the Season
The duration of the spring allergy season is increasingly influenced by dynamic environmental variables, leading to longer periods of high pollen exposure. Climate change is a primary driver, with rising global temperatures causing an earlier spring onset and a longer freeze-free growing period. Research shows that North American pollen seasons have lengthened by an average of 20 days over the last three decades.
This phenomenon, sometimes called “pollen creep,” means the window for tree and grass pollination is opening sooner than historical norms. Increased atmospheric carbon dioxide also acts as a fertilizer for plants, stimulating them to grow larger and produce higher concentrations of pollen. This boost contributes to more intense and prolonged allergic reactions.
Specific weather patterns can modify the season’s length and intensity in the short term. While light rain temporarily washes pollen out of the air, heavy spring thunderstorms can worsen allergy symptoms. Large raindrops cause intact pollen grains to rupture into smaller fragments, which are more easily inhaled and penetrate deeper into the lungs, effectively putting a higher concentration of potent allergens into the air.