How Does Pollen Cause Allergies

By Kathy Conner Cornell VCE Southside Master Gardener I have been dealing with a skin rash since Christmas. My doctor decided to do some bloodwork to see if something that is going into my body is causing the rash. One of the things that I have a high allergic reaction to is white oak Quercus alba, which we had joked that I can’t be allergic to that since that is the name of her practice. My master gardener mind couldn’t understand that because white oak is in the division Magnoliophyta - Flowering plants. Flowering plants have a pollinator relationship so are not wind pollinated or so I thought. I figured if I didn’t understand what is going on, maybe other folks didn’t either.
This white oak Quercus alba male flower is loaded with pollen that is wind driven and can cause allergic reaction in humans during flowering season. Many trees with inconspicuous flowers are wind pollinated. Photo from Virginia Tech Dendrology Gymnosperms like pines, junipers and cedars are wind pollinated. We have a row of eastern red cedars Juniperus virginiana along the pasture fence. On spring days we can see clouds of pollen blowing down the lane. We are all familiar with pine pollen that turns our cars green, our porches green and I swear even the cat looks a little green when the pine pollen blows. One would expect these pollens to be allergic triggers. From my research this is not the case. This pollen is so heavy it falls shortly after blowing. So. except for covering everything with pollen, it poses little problem to us. But what about these flowering plants? Turns out that plants with large flowers rarely cause any pollen allergies. Where do the trees fall in? We certainly don’t think of oaks as a flowering tree as we would a dogwood. I know our red maple is covered in bees when it blooms. The blooms are insignificant to us but the bees love them. According to the US Forestry Service “about 12% of the world’s flowering plants are wind-pollinated. Wind pollinated plants include grasses and their cultivated cousins, the cereal crops, many trees, the infamous allergenic ragweeds, and others. All release billions of pollen grains into the air so that a lucky few will hit their targets”. Other information in the Forestry Service article describe typical wind pollinated flowers. Wind-pollinated flowers typically have no bright colors, special odors, or nectar. Their flowers are small and most have no petals which expose their stamens and stigmas to air currents. Mother Nature has provided these plants with large amounts of pollen. The pollen is smooth, light and easily goes airborne. These plants are equipped with feathery stigma (female) to catch pollen from wind. Some may have staminate(male) and pistillate (female) flowers and may be monoecious or dioecious. They usually have single-seeded fruits, such as oak, grass, birch, poplar, hazel, dock, cat-tail, plantain, and papyrus”. Aha! This solves the mystery, not all plants in the Magnoliophyta - Flowering plants division are pollinated by insects, birds, bats, butterflies or flies. Some are wind pollinated. I am a big fan of Weather Underground. The biggest draw is that I get my weather not Danville’s or Lynchburg’s or even South Boston’s. Another feature is pollen count. If you click on the pollen box, it will show the level of pollen and list the trees, grasses or weeds causing the levels. According to The Asthma and Allergy Foundation of America common trees that cause pollen allergies are “Alder, Ash, Beech, Birch, Box Elder, Cedar, Eastern Cottonwood, Elm, Hickory, Juniper, Maple, Mulberry, Oak, Pecan, Poplar, Walnut and Willow”. All trees we have around here in abundance with the possible exception of the cottonwood. I’ve enjoyed doing this research and learning something new about plants. However, a pollen allergy could explain a runny nose, sneezing, watery eyes and coughing but doesn’t do a thing to explain why I have this rash! The VCE Halifax Extension Office is currently open Monday through Friday from 8 am to 5 pm. With the uptick in COVID cases in the county to HIGH risk, masks and social distancing are required. If you have gardening questions, you can continue to reach an Extension Master Gardener or Extension staff member by sending an email to or calling the Halifax Extension Master Gardener Help Desk at (434) 830-3383. Be sure to give us your first and last name, telephone number, email address if you have one and the nature of the call. The Help Desk phone is routinely checked. Someone will get back to you, although it may be from a different telephone number. When the spring allergies hit, remember it could be the trees that are causing the aggravation and if a rash is apparent, you may want to consult with your physician.