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Warmer weather is upon us here in the Northern Hemisphere. While it’s a welcome reward for surviving the winter to peel a few layers of clothing off, springtime is also when those unwelcome spring allergies start to blossom. If you do suffer from recurrent seasonal allergies, you aren’t alone. According to the American College of Allergy, Asthma, and Immunology, more than 50 million Americans experience various types of allergies each year. In fact, according to that same report, allergies are the 6th leading cause of chronic illness in the U.S. But that begs the question, what exactly is an allergy?

An allergy is a condition in which the immune system generates an abnormal reaction to an otherwise harmless substance. That substance is called an allergen, and it can take countless forms—dust mites, mold, grass, pollen, and different types of food can all illicit reactions in some people while having zero effect on others.

When you have an allergy to something, your immune system sees this substance as potentially harmful, and it reacts in a similar way to how it would respond to a dangerous virus or bacterium—however this time there’s nothing dangerous out there. Find out why the immune system performs this unnecessary act of rebellion in this week’s episode of Ask Us Anything.