Why Do We Have Allergies? How Our Bodies React to Spring

Along with warmer temperatures and spring blooms, this time of year brings a less welcome guest: seasonal allergies.

Common symptoms like watery eyes and runny noses are well known, but the reason some people develop reactions to certain substances remains something of a mystery, according to immunologist Ruslan Medzhitov.

"That is exactly the problem I love," Medzhitov, a professor at Yale University, told Discover magazine in April 2015. "It's very big, it's very fundamental and completely unknown."

A hornbeam blossom, photographed in April 2015, is a major source of pollen, which causes allergic reactions for millions of people. PHILIPPE HUGUEN/AFP/Getty Image

Related: Allergies: New Prevention for Cat, Dog and Hay Fever Reactions Discovered in Breakthrough Study

Many scientists believe allergies exist to defend our bodies against parasitic worms, but Medzhitov has a different theory: He believes the annoyance is a defense mechanism against poisonous substances, which isn't a well received idea.

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"I think the field will go around in that stage where there's a lot of resistance to the idea," he told the magazine. "Until everybody says, 'Oh yeah, it's obvious. Of course, it works that way.'"

Adding to the mystery is that people can go years before developing problems. However, there's growing evidence that genetics may play a role, and that somehow the condition is just triggered later in life.

"A person who has allergies triggered later in life would still have been born with the genetic predisposition, but for some reason they've had protective responses, and then something breaks that protection," Dr. Connie Katelaris, a professor at Western Sydney University, told The Guardian last year. "It's still not fully understood, but we believe the most common cause of later-life allergy is a significant infection, and that tends to trigger something in the immune system."

The mechanisms for how allergies impact our bodies are better understood. According to the American Academy of Allergy Asthma & Immunology, reactions happen when a person's immune system looks at harmless substances, like pet dander, as a potential threat. The immune system then produces antibodies that release chemicals like histamine to cause the reaction.

Unfortunately, there is no stopping those pesky allergies, but steps can be taken to better manage symptoms. Experts advise staying indoors on high pollen-count days, rinsing off as soon as you get home and washing your sheets weekly, NBC reported. Check the pollen count for your area at the American Academy of Allergy Asthma & Immunology website.