Ah, springtime. The season of cherry blossoms, baseball and birdsong, not to mention itchy eyes, red noses and sore throats.

If complaints about seasonal allergies seem worse this year, it may not be all in your head. A study presented at the annual meeting of the American Chemical Society, which began Sunday, found that two common pollutants interact with a major pollen allergen at a chemical level, creating an extra-potent immune trigger capable of turning even the most stalwart of spring-lovers into a sniffling puddle of mucus.

Allergic rhinitis — or nasal allergies — afflicts between 10 percent and 30 percent of the global population, according to the World Health Organization, and that proportion is on the rise. Scientists have long suspected that the increasing prevalence of allergies was linked to air pollution and climate change, but they didn’t have an explanation how that process took place, said the study’s co-author Ulrich Poschl, who works at the Max Planck Institute for Chemistry in Germany.

“Our research was to explore mechanistically how that all works,” Poschl said in a phone interview with The Washington Post.

Using laboratory tests and computer simulations, Poschl and his colleagues looked at how ozone (a main component of smog) and nitrogen dioxide (found in car exhaust) interacted with a birch pollen allergen called Bet v 1.

The combination was tremendous — for the allergens at any rate, less so for the stuffy-nosed people who suffer from them. The researchers found that ozone sets off a chain of chemical reactions that changes its protein structure. The altered allergen is then more likely to bond with nitrogen dioxide, which exacerbates immune response. (Allergies occur when the body’s immune system is hypersensitive toward irritants, called allergens, that would otherwise be harmless.) Even when the ozone-altered allergens don’t react with nitrogen dioxide, two of them can bond with one another, forming a larger molecule that is extra-irritating to the immune system.

Whichever way the chemical reactions play out, combined effect of both pollutants is to make allergens particularly powerful, especially in humid, hot and smoggy environments, Poschl said.

The study, which is considered preliminary since it has not yet been published in a peer-reviewed journal, added that the pollutants’ impact on allergies goes beyond the chemical level. By contributing to climate change, air pollution helps raise average temperatures and prolong the pollination season. These factors also exacerbate spring allergies by making pollen more common and more potent.

Poschl, who supports global action on climate change, said he hopes the study will add to the pressure to reduce all kinds of pollution.

“Humans are not just affecting but shaping the environment … it’s actually unreasonable to assume that it would not affect humans with our highly delicate immune system,” he said. “That’s the background motivation for these kinds of studies.”