The study in Norway examined the relationship between pollen levels, hay fever and exam performance and suggested rising pollen levels could push down results by 10% for hay fever sufferers.
Report author Simon Sobstad Bensnes suggested the findings showed that students could be "unfairly barred" from getting into university.
"Holding high-stakes exams during pollen season has a large negative effect on allergic students, who are subsequently unfairly barred from enrolling in the most prestigious universities," said Prof Bensnes.
"Increases in pollen counts can temporarily reduce cognitive abilities for allergic students, who will score worse relative to their peers on high stake exams, and consequently be at a disadvantage when competing for jobs or higher education."
The study, from the Norwegian University of Science and Technology, examined the impact on hay fever sufferers of taking exams at a time of year when pollen levels are higher. Using the results of public exams in Norway over three years, researchers found that on days with high pollen levels exam performance was consistently lower.
There was an average performance dip of 2.5% on high pollen days - and researchers estimate that for pupils with an allergic reaction results were lowered by about 10%.
About one in five people are estimated to suffer from hay fever - and the study says that this could be higher among young people, with suggestions that a quarter of young people in Norway are allergic to some extent.
In England's exam system, pupils who have had serious problems with hay fever on an exam day could ask for this to be taken into account by examiners. The report author says it raises questions about holding exams in the spring and the early summer, when sufferers are most likely to be affected.