Allergies occur when your immune system reacts to a foreign substance (allergen) that doesn't cause a reaction in most people. Common allergens include pollen, dust mites, mold, pet dander, and certain foods. Symptoms can include sneezing, itching, runny nose, watery eyes, and in severe cases, anaphylaxis. Management strategies include avoiding triggers, medications (antihistamines, decongestants), immunotherapy, and emergency preparedness.