Seasonal allergies occur when your immune system overreacts to normally harmless airborne particles. An allergy is an abnormal hypersensitivity to these airborne particles or environmental antigens called allergens. An allergen can include pollen from trees, grasses, weeds, and ragweed, as well as cat or dog dander, dust and moulds. Exposure to an allergen leads to overactive B cells that in turn produce excess Immunoglobulin E (IgE). IgE then triggers the allergic symptoms by activating mast cells (cells that line the mucous membranes of the eyes, nose and throat) that produce histamine. Common symptoms include: runny nose, sinus congestion, headache, fatigue and itchy eyes.

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