Allergies begin when your immune system mistakenly identifies a harmless substance, such as pollen, as something that’s dangerous for your body. Then every time you encounter that substance, you have an allergic reaction.

Some of the most common allergens include:

  • Airborne allergens: mold, dust, pet dander, and pollen from plants and flowers
  • Contact allergens: poison ivy, nickel, latex, soaps
  • Food allergies: milk, eggs, peanuts, wheat, tree nuts, soy, fish, and shellfish
  • Insect stings: bees, wasps, and hornets
  • Medications: penicillin, aspirin, ibuprofen

Children and adults who have food allergies also have a higher risk of developing allergic rhinitis (hay fever) and atopic dermatitis (eczema).