An allergy is when your immune system overreacts to a normally harmless substance like pollen, pet dander, certain foods, or insect stings. When someone with allergies encounters their trigger (called an allergen), their body releases chemicals like histamine that cause symptoms ranging from sneezing and itchy eyes to hives and breathing difficulties. Allergies are extremely common, affecting millions of Canadians. While most allergies cause discomfort rather than danger, some people have severe allergies that can trigger life-threatening anaphylaxis. Treatment includes avoiding triggers, taking antihistamines, or receiving allergy shots for long-term management.