Seasonal allergies such as hay fever may not only give you a stuffy nose and itchy eyes, but also change your brain, a new study has warned.
Scientists found that brains of mice exposed to allergen actually produced more neurons than controls, they did this using a model of grass pollen allergy.
The research team examined the hippocampus, the part of the brain responsible for forming new memories, and the site where neurons continue to be formed throughout life.
During an allergic reaction, there was an increase in the numbers of new neurons in the hippocampus, researchers said.
The formation and functioning of neurons is linked to the brain's immune cells, the microglia.
The scientists found that the same allergic reaction that kicks the body's immune system in high gear, has opposite effect on resident immune cells of the brain.
The microglia in the brain were deactivated in brains of these animals.
"It was highly unexpected to see the deactivation of microglia in the hippocampus," said Barbara Klein, from the University of Salzburg in Austria.
"Partly because other studies have shown the reverse effect on microglia following bacterial infection," said Klein, one of the authors of the study.
"We know that the response of immune system in the body is different in case of an allergic reaction versus a bacterial infection. What this tells us is that the effect on the brain depends on type of immune reaction in the body," she said.
According to a report by the World Health Organisation (WHO), 10-30 per cent of the population worldwide suffers from allergic rhinitis, commonly called hay fever.
Allergic reaction also causes an increase in neurogenesis, the growth and development of nervous tissue, which is known to decline with age, researchers said.
The study was published in the journal Frontiers in Cellular Neuroscience.
