An allergic reaction, also known as a hypersensitivity reaction, is caused by the immune system in response to a foreign substance, or allergen. When the body recognizes a substance as foreign, it prepares an attack to destroy the substance. These substances are released to fight the foreign molecules or mark them for destruction. The body has more than one way to deal with foreign matter, only one of which is an allergic reaction. Another reaction is called an adverse physical reaction.
Many people confuse the two types of reactions.
Adverse reactions reflect the body's inability to process the foreign substance without stomach pain, anxiety, heartburn, dizziness, or other symptoms. In general, antihistamines and other allergy medications do not relieve the symptoms of adverse physical reactions. Antihistamines are used to relieve the symptoms of allergic reactions, which do involve the histamine system. How the Immune System is Supposed to Work The immune system uses antibodies to fight infection by foreign bodies, such as bacteria and allergens. For example, IgE antibodies are proteins produced by B-lymphocytes .