Why Are My Allergies Worse in Some Years?

Why Are My Allergies Worse in Some Years?

An aerobiologist explains why last summer’s weather is critical to this spring’s pollen

By Heidi Mitchell in the Wall Street Journal

Every year, it seems, weathermen claim this will be the worst allergy season ever. While that is highly unlikely, seasonal allergies, which affect some 30% of Americans, do vary widely from year to year. One expert, Estelle Levetin, a professor of biology at the University of Tulsa, explains how a long winter can be a boon for people with hay fever and why last summer’s weather is critical to this spring’s pollen.

The big picture

The length and strength of allergy season—generally reactions to tree, grass or weed pollens—largely depends on weather, both day to day and season to season, says Dr. Levetin, who specializes in aerobiology. “If the summer prior was hot and dry, then the dormant winter tree buds will be stressed and have fewer flower buds during the spring warm-up,” bringing a positive outcome for people with hay fever, she says. Similarly, a harsh winter can also reduce pollen load by damaging dormant tree buds. And a rainy spring might wash out the tree pollen—also a bonus for allergy sufferers.

On the other hand, a dry spring with sunny skies and nice breezes are the optimal conditions for pollen to be released and spread. When winter is long and spring is short, as has been the case this year in places like Oklahoma, where Dr. Levetin lives, “everything can seem to bloom at once,” she says. The result: lots of itchy eyes and drippy noses.

Elm, grass, cedars, oaks, mulberry, cottonwood and ragweed are some of the most common plants whose seasonal pollen triggers allergic reactions. “But the levels at which people are affected is individual,” says Dr. Levetin a fellow with the American Academy of Allergy, Asthma and Immunology.

Let it rain

Recent torrential downpours in the Midwest have wreaked havoc in places, but have been an advantage for people with pollen allergies. “Rain in the spring will wash out tree pollen, making the season easier,” Dr. Levetin says. However, the rains also could make growing conditions good for summer grasses and weeds, making those seasons worse, she says. Most allergists consider pollen from ragweed, which blooms in late summer and fall, the biggest problem when it comes to allergy triggers, she says.

Rain also affects how much pollen is floating around day to day. High-pollen days can alternate with low-pollen days when it pours. “The allergy season is so weather-driven, short term and long term,” Dr. Levetin says. “And it varies from region to region.”

Global patterns

Allergy season in the Northern Hemisphere typically runs from February or March through October. Dr. Levetin’s aerobiology lab found in a published study that the length of spring-tree allergy season can vary by as much as 40 days depending on the weather conditions of the prior winter. Predicting how bad a coming allergy season will be is difficult, since an unforeseen drought or strong rains can quickly throw off projections, she says.

Dr. Levetin says many climate scientists expect global warming will cause greater variability in weather patterns, making predictions even more difficult-and allergy seasons even more random. “In Northern states, where global warming is already having an effect, winter is shorter and spring might come a little earlier, and that can lengthen the pollen season,” she says. “Of course, there are exceptions. This winter, for example, was longer in the Northeast.”

People who suffer badly from pollen allergies can always hope for favorable weather. A dream year: “A long winter and rain in the spring—so long as you’re not allergic to mold,” Dr. Levetin says.