Alerji, or allergy, is a condition where the immune system reacts abnormally to substances that are usually harmless, known as allergens. Common allergens include pollen, dust mites, pet dander, and certain foods like nuts or shellfish. Symptoms can range from mild, such as sneezing and itching, to severe, including difficulty breathing or anaphylaxis. When a person with an allergy encounters an allergen, their immune system mistakenly identifies it as a threat and produces antibodies called IgE. This triggers the release of chemicals like histamine, leading to allergic reactions. Treatment options include avoiding allergens, taking antihistamines, or receiving allergy shots for long-term relief.