Seasonal allergies, also known as allergic rhinitis, are an exaggerated immune response to harmless airborne substances, primarily pollen. This reaction causes symptoms like sneezing, congestion, and itchy eyes. For Pennsylvania (PA) residents, understanding the timing and specific triggers of these seasonal events is essential. The allergy season in PA is a sequence of distinct phases driven by the life cycles of local plants.
The Three Phases of Allergy Season in PA
The allergy year in Pennsylvania begins early in the spring with the release of tree pollen, sometimes starting as early as February. This phase typically continues until late May, with common PA tree allergens including oak, maple, birch, hickory, and walnut. Tree pollen concentrations often peak in April, causing significant symptoms across the state.
As tree pollen subsides toward the end of spring, the summer allergy season begins, dominated by grass pollen. Grass pollination generally starts in late May or early June and lasts until mid-August. Common grass culprits include Timothy, Kentucky bluegrass, fescue, and orchard grass.
The final phase of the pollen season is triggered by weeds, beginning in mid-August and continuing through the fall. Ragweed is the dominant allergen during this time in Pennsylvania; a single plant can release a billion grains of pollen that travel long distances. Ragweed season typically peaks around Labor Day and persists until the first hard frost, which ends the pollen release.
Regional Differences and Microclimates
The generalized timing of Pennsylvania’s allergy season is subject to significant variation due to the state’s diverse geography and microclimates. Areas in Eastern PA, such as the Philadelphia region, often experience an earlier onset of spring tree pollen. This is because these lower-elevation, more urbanized areas tend to have warmer temperatures sooner in the year.
Conversely, Western PA regions, like the Pittsburgh area, or locations near higher elevations may experience a slightly delayed start to the spring season. Colder air masses and higher altitudes can push the start of tree and grass pollination back by a few weeks compared to the southeast. While rural areas have a higher concentration of pollen-producing vegetation, urban centers like Scranton are often challenging for allergy sufferers because air pollution can interact with pollen particles, exacerbating symptoms.
Factors Influencing Allergy Season Severity
The intensity of any given allergy season is not constant and is largely influenced by environmental variables. Warmer winters and early spring temperatures are linked to an earlier start and a longer overall duration for all three pollen seasons. Research suggests that pollen seasons are starting earlier and lasting longer than they did several decades ago, a trend often associated with climate change.
Rainfall plays a dual role in pollen counts; heavy rain provides temporary relief by washing pollen out of the air and grounding it. However, a period of dry, windy weather following a rain event can rapidly spread accumulated pollen, causing a sharp increase in counts. Ultimately, the first hard frost marks the conclusion of the weed pollen season, offering reprieve from outdoor pollen until the following spring.