Learn how the immune system defends against foreign substances and what happens when it overreacts, causing allergies. This video explains the role of antigens, antibodies, and the types of hypersensitivity, with a focus on type one or immediate hypersensitivity. Discover how allergens like pollen trigger allergic reactions, the severe consequences of untreated reactions, and the treatments available, from antihistamines to EpiPens. Understand the importance of managing exposure to allergens and the potential need for desensitization in cases where alternative treatments are unavailable.