Allergens are substances that can trigger an allergic reaction in some people. Common allergens include pollen, dust mites, pet dander, certain foods like peanuts and shellfish, and insect stings. When a person with an allergy comes into contact with an allergen, their immune system mistakenly identifies it as harmful and reacts, leading to symptoms such as sneezing, itching, or swelling. The severity of allergic reactions can vary widely among individuals. Some may experience mild symptoms, while others could face life-threatening conditions like anaphylaxis. Avoiding known allergens and seeking medical advice are essential steps for managing allergies effectively.