Trees and flowers in full bloom Sunday with pollen levels taking off. (Zsaj/Flickr)

If you’ve been sniffling, sneezing and wheezing more than usual this week, we have an explanation.

Propelled by mild temperatures, partial sunshine and gentle breezes, tree pollen levels have leaped to their highest level of the year. The U.S. Army Centralized Allergen Extract Lab in Silver Spring, Md., which measures the amount of pollen in the air, reported the tree pollen count spiked to 1,695.85 grains per cubic meter of air Tuesday. This is a “very high” count, according to Susan Kosisky, a microbiologist who directs the lab.

“Oak, sycamore, pine, birch and sweet gum pollen lead the list of allergenic tree species out and about at high concentrations,” Kosisky wrote in the lab’s most recent report. “The yellow film on outdoor surfaces really starts to build up when these tree species release enormous amounts of pollen into the air.”

In an email interview, Kosisky said Washington averages around three to four days each year when tree pollen counts climb at least as high as it was Tuesday. In some years, the tree counts have even reached concentrations two to three times higher.


Washington's peak tree pollen counts by year. (Susan Kosisky)

When pollen counts surge like this, oak trees are the main offender.

Oaks account for “close to 50 percent of the total annual tree pollen production,” Kosisky wrote, noting that these trees, as well as several other species, have just started releasing their pollen grains. “Many of our abundant tree pollen producers are also not quite at peak level concentrations, to include pine, birch, mulberry, sycamore and ash. . . . Thus, I would suspect with weather permitting — there is still plenty more in store for us.”

Wednesday’s jolt of tree pollen arrived right around the normal time. Historically, counts have peaked around the third or fourth week of April. But warm weather can bring the pollen out early, while cold weather can delay it.

This spring, temperatures have averaged a touch above normal but with a fair amount of volatility, so the release of pollen has been a bit uneven.


Time series of 2019 tree pollen levels compared to average. (Susan Kosisky)

There was a pollen spike in the second week of March from some of the early pollinating trees as temperatures warmed into the mid- to upper 70s. “Warm temperatures near 80 degrees and sunshine are the perfect ingredients to set our tree counts soaring,” Kosisky said.

But in early April, we had chilly nights with lows in the 30s and 40s, and pollen levels were “considerably below average,” Kosisky said.

She added that when pollen levels are depressed for a time, they have a tendency to “catch up” once warmer weather arrives. Since April’s second week, temperatures have averaged above normal, and pollen levels have been off to the races. Our eyes, noses and lungs are paying the price.

Tree counts should start to come down in May, but then grass counts start ascending.