An allergy is a sensitivity to a substance that is normally harmless. Flowers, trees, a family pet, or dust are examples of things that can cause an allergy. Even foods like peanut butter, fish, and milk can cause an allergic reaction in sensitive people. A substance that triggers an allergy is called an allergen.
People can have different reactions to allergens, even when they are allergic to the same things. For example, an allergen that causes eye inflammation in one person may cause headache in another. Some common reactions a person might experience after contact with an allergen include:
asthma â€¢ hay fever â€¢ upset stomach â€¢ eye inflammation â€¢ eczema (a skin disease) â€¢ itching â€¢ itching of the roof of the mouth â€¢ itchy ears, nose and throat