Seasonal allergies (allergic rhinitis) result from the body’s immune system overreacting to airborne particles like pollen. For Seattle residents and visitors, understanding the local allergy schedule is the first step toward symptom management. Seattle’s temperate, mild climate creates a unique environment for plant life, resulting in an allergy season that is often prolonged and begins earlier than in many other parts of the United States. This extended schedule means that individuals sensitive to pollen may experience symptoms across three distinct seasons instead of a single springtime event.
The Seattle Allergy Calendar
The allergy season in the Puget Sound area progresses chronologically, starting in late winter and extending into the fall. Tree pollen marks the beginning of the cycle, often commencing as early as late February or early March, driven by the region’s mild winters. This initial phase continues through the end of May, representing the most intense period for many allergy sufferers in the city.
As tree pollen levels decline, the next phase transitions to grass pollen dominance from late May or early June through July. This mid-year period brings a new set of challenges, particularly in parks and open grassy areas where the primary culprits are most abundant. Following the summer, the final phase arrives with weed pollen, which typically peaks from August through October. Although the intensity can vary, this structure defines an allergy calendar that spans approximately eight months of the year.
Primary Local Pollen Triggers
Tree pollen is the most potent and earliest allergen in Seattle, with multiple species contributing to high counts in late winter and early spring. Alder trees are particularly notorious for their massive pollen output, often signaling the start of the season in February. Birch and Maple trees follow closely, becoming major producers, with Birch pollen peaking around mid-April to mid-May. Other common tree allergens like Cedar, Juniper, and Oak also contribute significantly to the high spring counts.
As temperatures rise, the focus shifts to grass species; Ryegrass and Timothy grass are common sources of summer irritation. These grasses release their pollen throughout the warmer months, affecting individuals who spend time outdoors in residential lawns or natural meadows. In the late summer and fall, weed pollen takes over, with Ragweed being the primary offender, although it tends to be less widespread in Western Washington compared to the Midwest. The damp conditions of the Pacific Northwest also promote the growth of mold spores, which become a prominent allergen in the fall as leaves decay and moisture increases.
Unique Regional Climate Factors
Seattle’s unique geography and weather patterns significantly shape the local allergy experience. The consistently mild and moist climate prevents the prolonged, deep freezes that would otherwise delay or destroy early-budding plant life. This lack of a harsh winter allows trees to begin their reproductive cycles much sooner, pushing the start of the allergy season into late February. The ongoing effect of climate change also contributes to this extension, with local data suggesting the pollen season is starting earlier and lasting longer than in previous decades.
The frequent rain characteristic of the region has a dual effect on pollen levels, often referred to as the “Pollen Wash.” While heavy rain temporarily scrubs pollen from the air, providing immediate relief, the ample moisture simultaneously encourages lush, rapid plant growth, quickly replenishing the pollen supply. The geographical basin of the Puget Sound can also lead to periods where pollen is trapped, concentrating allergens in the air during dry, calm spells.
Managing the Local Season
Effective management of Seattle’s extended allergy season begins with staying informed about real-time pollen levels in the region. Local resources, such as reports from the Northwest Allergy and Asthma Center or weather services, provide daily counts that allow for planning outdoor activities. On days when tree pollen is peaking, keeping windows closed in the car and home prevents the influx of millions of microscopic grains. Running an air conditioning system with a high-efficiency particulate air (HEPA) filter can also significantly reduce the indoor allergen load.
Because the damp climate encourages mold growth, controlling indoor humidity is important. Using a dehumidifier to keep indoor air below 50% humidity can mitigate the buildup of mold spores, which are a major trigger in the fall. Simple behavioral adjustments, like showering and changing clothes immediately after spending time outdoors, helps remove pollen that has settled on hair and fabric. Preemptive use of over-the-counter or prescription allergy medications, as advised by a healthcare provider, can help control symptoms before the seasonal peaks arrive.