Pollen seasons are starting to last longer in Washington

Published 1:30 am Friday, July 10, 2026

Pollen levels are increasing significantly over time in the Seattle-Puget Sound area, marking one of the most affected areas nationwide for rising seasonal allergen levels.

The March 2026 Allergy Capitals report with the Asthma and Allergy Foundation of America (AAFA) indicated that Seattle has worse-than-average overall pollen for the year.

More than 106 million people in the United States have allergies and/or asthma, per AAFA. These allergies and asthma can be intensified by the pollen season. Due to the impact of climate change, symptoms hit harder and last longer, with some parts of the nation experiencing pollen allergies year-round.

The top allergy capitals of the country have typically been concentrated in the Southeast region of the U.S. due to warmer, more humid climates. However, in 2025, the Western region of the U.S. began to experience spikes in longer pollen seasons and pollen amounts, especially for grass and weed pollen.

There are three weather phenomena that play a significant role in last year’s pollen levels, AAFA says. These are atmospheric rivers, warmer temperatures and droughts.

In Washington, 45 atmospheric rivers impacted the state during the 2025-2026 year, with the most extreme taking place in December 2025, when historical and widespread flooding and rainfall affected Western Washington, per the Center for Western Weather and Water Extremes.

These rivers in the sky contribute to increased pollen, due to the long, narrow bands of water vapor that they consist of. When these rivers reach land, they bring heavy rain, strong winds and sudden changes in temperature.

Over the past 50 years, atmospheric rivers have intensified, per AAFA. Warmer air holds moisture, and climate change is expected to further increase the intensity of these rivers, leading to an earlier start in pollen seasons, higher peaks and longer exposure for people with allergies.

As the ground warms up in the late winter and spring, trees begin to release pollen. Weed pollen can continue into the fall, until the first freeze. Overall, as temperatures increase over the years, spring arrives earlier and the first frost comes later in the fall, increasing the length of the pollen season.

The very first pollen to appear each year that causes the most spring allergy symptoms is tree pollen. Trees have been producing larger amounts of pollen in recent years, according to AAFA. The most pollen production from trees is typically February through April, but they can begin producing pollen as early as December and January.

While there are various types of tree pollen, some of the most common in Western Washington and Kitsap County are large pollen, visible to the eye as a fine yellow dust that covers outdoor surfaces. The yellow dust primarily comes from coniferous trees, like pine. Other conifers like spruce, fir and cedar, all abundant in the Pacific Northwest, produce the same heavy yellow pollen grains. This type of pollen falls near the tree, but there are other forms of pollen that are not visible to the eye and lighter, making it easier for the wind to carry and to negatively affect those with allergies.

In May 2025, the Washington State Department of Health reported that the pollen season in Washington starts almost three weeks earlier and lasts about a month longer than it did 30 years ago. More specifically, in Kitsap County, grass pollen levels are consistently high from late May or early June to July, with the peak in June.

Kitsap County tracks PM2.5 (particulate matter smaller than 2.5 micrometers in diameter), which is a very small air pollutant linked to respiratory health. Higher PM2.5 levels are linked to higher emergency department visits, per the Kitsap Public Health District. Although whole pollen grains are too large to be counted as PM2.5, broken pollen fragments and other plant debris can become small enough to contribute to PM2.5 pollution as well.

KPHD shared that poorer air quality, as measured by PM2.5, has historically corresponded with increases in asthma-related emergency department visits in Kitsap County. The current available public data runs through the end of 2024, and KPHD shared that they plan to update their dashboard later this summer.

The DOH also partners with 10 statewide monitoring sites to track real-time pollen data. Anyone can view local pollen counts and specific allergen forecasts by using the PollenWise App.