Ready for Spring Allergies? Here’s What You Need to Know

As spring arrives and temperatures warm, trees blossom and release pollen — the fine, yellow powder that covers cars, patios and other outdoor surfaces.

Pollen is crucial to a tree’s reproduction, as it contains the male reproductive cells necessary to fertilize the female part of another tree.

However, while important for tree reproduction and the ecosystem, tree pollen is often the cause of most spring allergies, triggering symptoms like sneezing, runny nose, itchy eyes and more.

Robert Bardon, a professor of forestry and environmental resources at NC State, has been tracking tree pollen production in Raleigh and the surrounding area for nearly a decade.

Bardon said that while the timing of tree pollen production fluctuates every year, he has noticed it starting earlier — sometimes by a week — and lasting longer.

We recently asked Bardon about tree pollen production and why it causes so much discomfort for allergy sufferers. Check out the Q&A below to learn more.

How long does the spring pollen season last in North Carolina? 

For trees, the pollen season runs from February through the end of May. Species such as juniper, maples and elm are often some of the first to produce pollen, followed by pines, oaks, hickory and ash. Production starts slowly, but by mid-March we see sharp increases in the production of pollen. The peak of the tree pollen season occurs at the end of March and into the first week of April and then tapers off from there. 

What kind of tree pollen is the most prevalent and allergenic in the spring? 

Hardwood tree pollen is often considered more allergenic than pine pollen. Hardwood tree pollen is more allergenic because the pollen grains are smaller and lighter than pine pollen grains, making them easier for the wind to carry and inhale. Pine pollen grains are also much smoother compared to hardwood trees, such as maple and oak, which produce a fine grain pollen that’s also quite rough. The smoother the grain the less likely to be an irritant.

If pine tree pollen is larger, does that make it more visible?

Pine pollen is much more visible because it is larger in size and it is yellow in color. Pines produce larger pollen grains than hardwood trees, often two to three times larger. For example, a pine pollen grain can range in size from 0.06-0.1 millimeters, where oak pollen grains are approximately 0.03 millimeters in size. 

When are pollen counts highest and lowest during the day?

Tree pollen counts tend to rise after sunrise, peaking in the mid-morning, then tapering off in the afternoon. The cooler, more humid conditions of early morning reduce the dispersal of tree pollen, often keeping it lower in the atmosphere. As the air dries out and temperature rises, wind currents pick up, lifting pollen into the atmosphere and dispersing it across the landscape.

What factors can cause pollen counts to fluctuate in the spring?

Environmental factors that can influence pollen counts include temperature, wind and precipitation. Temperatures that are conducive to plant growth often lead to much higher production of pollen. If we have mild temperatures, above freezing, we often have conditions favorable to the production of pollen. If we end up with a late season frost that results in damage to the trees male flowers, we can see a reduction in pollen production. Wind impacts the dispersal of pollen. On dry, warm, windy days we often see higher pollen counts as wind stirs up and disperses the pollen. Precipitation and humidity often have a negative impact on the dispersal of pollen grains. Very humid mornings often result in the pollen grains being weighed down, potentially reducing the amount of pollen being dispersed in the atmosphere. Rain washes the pollen out of the atmosphere, temporarily reducing the pollen count.

How are pollen levels measured and how can you view the daily pollen count?

Pollen counts are conducted by the North Carolina Department of Environmental Quality. The agency uses a pollen sampler that samples the air one minute out of every 10 minutes. Pollen is collected on the device and analyzed to determine the total number of pollen grains per cubic meter of air sampled. To learn more about the sampling method or to see the most recent pollen report, visit https://www.deq.nc.gov/about/divisions/air-quality/air-quality-monitoring/pollen-monitoring.