Oregon’s lush landscapes and mild, moist climate contribute to an intense and prolonged allergy season. Seasonal allergies here are not a single event but a complex, nearly year-round cycle driven by a succession of airborne plant pollens. Due to the state’s diverse geography, the period of exposure to allergens is significantly extended compared to many other parts of the country. This consistent presence of irritants means the “allergy season” is a dynamic challenge demanding vigilance from late winter through late fall.
The Annual Cycle of Airborne Pollen in Oregon
The seasonal allergy cycle in Oregon begins exceptionally early with tree pollen, often starting in the heart of winter. Species like Cedar and Pine can begin pollinating as early as December, with the main tree season starting in January. Hazelnut (filbert) trees are notable early triggers, typically releasing pollen in late January and February, especially in the Willamette Valley.
As temperatures rise in late winter and early spring, the tree pollen count skyrockets with the addition of Alder, Birch, Maple, and Oak. The peak of the tree pollen season generally hits in March and April, leading to the most intense symptoms. This wave of allergens usually tapers off by the end of May or early June, making way for the next seasonal shift.
The second wave is dominated by grass pollen, which begins to rise in late spring and typically reaches its peak intensity from Memorial Day through July. Grasses like Ryegrass, Fescue, and Orchard grass are the primary culprits during this time. This period is challenging due to the sheer volume of grass pollen released into the air.
The weed pollen season takes over in late summer and early fall, running from late August until the first heavy frost. Prominent weed allergens include Ragweed, Sagebrush, and Nettles. This outdoor pollen season can persist well into October and November, bridging the gap until winter.
How Geography Impacts Local Allergy Timelines
The timing and severity of pollen seasons fluctuate greatly depending on the specific microclimate of an Oregon region.
Willamette Valley
The Willamette Valley, encompassing Portland, Salem, and Eugene, is an allergy hotspot due to its agricultural landscape and topography. The valley cultivates a significant portion of the nation’s grass seed, leading to exceptionally high concentrations of grass pollen during the summer peak. Its geographic enclosure, bordered by the Coast Range and the Cascades, often traps airborne pollen, amplifying the season’s intensity.
Coastal Region
The Coastal Region often experiences a delayed and milder pollen season, particularly for tree and grass pollens. The consistent oceanic influence and cooler temperatures slow down the biological cycles of plants compared to inland areas. While the coast may offer temporary relief from inland pollen peaks, the persistent dampness can contribute to different year-round issues, such as mold.
Eastern and High Desert Oregon
In Eastern and High Desert Oregon, the allergy season is shorter but intensely concentrated once it begins. The higher elevation and drier climate mean that spring thaw and plant growth start later than in the western valleys. Primary triggers include high-desert plants like Sagebrush in the fall and localized grasses in the summer. The timing of the season is closely tied to snowmelt and temperature, often pushing allergy peaks later into the calendar year.
Year-Round Allergy Triggers Beyond Pollen
While the pollen cycle dictates seasonal allergies, many Oregon residents suffer from year-round triggers. The state’s cool, damp climate creates an ideal environment for the proliferation of mold and fungal spores. Outdoor mold thrives in wet, decaying organic matter, and levels can spike in late fall, winter, or after extended rain events.
Indoor mold is also a concern, flourishing in damp basements, bathrooms, and poorly ventilated homes. These microscopic spores cause respiratory symptoms that mimic pollen allergies, offering no break during the off-season. This fungal activity often becomes the primary trigger when the pollen count has dropped.
Common indoor allergens like dust mites and pet dander are perennial issues that become more problematic when people spend increased time inside. Dust mites thrive in the humid, mild conditions common to Oregon homes, making them a constant presence. As windows stay closed and heating systems recirculate air in the colder months, the concentration of these indoor irritants rises, exacerbating lingering respiratory symptoms.