Allergies happen when the immune system reacts to a foreign substance that gets inside the body. These substances are known as allergens. They include pollen, bee venom and pet dander. Allergies also can happen due to certain foods and medicines that don’t cause reactions in most people.

The immune system makes protective proteins called antibodies that attack invaders such as germs. But with allergies, the immune system makes antibodies that mark a specific allergen as harmful, even though it isn’t. Coming into contact with the allergen causes an immune system reaction that can inflame the skin, sinuses, airways or digestive system. Allergic reactions vary from person to person. They can range from minor irritation to a life-threatening emergency called anaphylaxis.

While most allergies can’t be cured, treatments can help relieve your allergy symptoms.When you think of allergies, maybe you think of tree pollen. Or perhaps pet dander. Or nasal congestion. The fact is, allergic rhinitis, the technical name for hay fever, can be triggered when you breathe something you’re allergic to–be it pollen, pet dander, dust, or mold. And just because the allergens happen to be breathed through your nose, doesn’t mean your nose is the only place you’ll experience allergy symptoms.