Nothing to Sneeze at: Allergies May Affect the Brain

Do you feel like you become a different person come spring and fall? Do your eyes burn red and your orifices drip? Do you make violently loud exclamations without warning?

You, of course, have seasonal allergies, caused by things like pollen from different trees, grasses and weeds. And you're in good company. According to the American Academy of Allergy Asthma & Immunology, between 10 and 30 percent of the world's population has allergic rhinitis, or hay fever.

New research indicates that those pesky allergies might be doing something to change your brain. A small study by a team of Austrian scientists found that 10 mice that were exposed to an allergen from a common grass produced more neurons in the hippocampus than the control group of nine mice. (The hippocampus stores-long term memories and makes new neurons, among other tasks.) Those 10 mice also had fewer and less active immune cells in the same region.

Those immune cells in the brain are called microglia, and the researchers found they were deactivated in the hippocampus of the allergic mice. It was a bit of a surprise to researchers, who had seen in other studies that bacterial infection caused the opposite effect. It was also surprising because an allergic reaction is essentially your body's immune system overreacting, so why wouldn't these particular immune cells heed the call? Could it be to protect the hippocampus? Either way, it tells us that the brain doesn't react to all infections in the same way.

And what's up with the hippocampus getting busy making even more neurons in the allergic mice? Is it good news for the brain's ability to learn and make memories? Do allergies somehow affect memory?

As you've probably guessed, the researchers don't know what it all means. More studies need to be done to see if those two behaviors in mice are beneficial or dangerous for the central nervous system and hippocampus. But this study does join a growing pile of research linking allergic reactions to more than just runny noses and watery eyes.