Why You’re Getting Allergies for the First Time

What causes seasonal allergies to develop? Seasonal allergies are reactions to environmental elements like pollen or mold spores that tend to swirl around in the air during certain times — such as in the spring, when plants pollinate. When you’re allergic to something like pollen, your immune system perceives it as a threat and triggers a chain reaction at the point of exposure. Antibodies in the nose or lungs stimulate the release of chemicals like histamine, which can lead to the sneezing, runny nose or congestion. Scientists aren’t exactly sure why you can develop new allergies or symptoms without ever having had them before, but there are several potential causes. For one, climate change is causing allergy season to start earlier and last longer, so it makes people more prone to developing symptoms, experts said. In addition, some infections (like colds) could compromise protective mucous membranes, which could in turn weaken the body’s ability to keep allergens from triggering the immune system, said Dr. Alkis Togias, a branch chief at the Division of Allergy, Immunology and Transplantation at the National Institute of Allergy and Infectious Diseases. Where you live, and how long you’ve lived there, may matter as well. For some people, moving to a new place can bring a reprieve, if they’re no longer exposed to the allergens that used to trigger their symptoms. But for others, it can introduce new problems, said Dr. Caroline Sokol, a principal investigator at the Center for Immunology and Inflammatory Diseases at Massachusetts General Hospital. Some may see their seasonal symptoms initially disappear — typically for about three to five years. “Then all of a sudden, the allergies come back in full force,” she said. “But now they’re directed against new pollens.” Living in the same place for a long time can also factor in. Prolonged exposure to irritants like pollen may actually increase the risk of allergies, as the body gradually builds an immune response to a substance it continually encounters, Dr. Sokol said.