The term allergy denotes a hypersensitive response within the body, to certain substances known as allergens. The allergen is not necessarily harmful in itself and most people do not respond adversely to the allergens. But people who develop hypersensitive response to the allergen can develop several symptoms, some of which can even be life threatening.
Any substance (natural or synthetic) can trigger an allergic response. During an allergic response the immune system activates the small lymphocytes known as the T cells and B cells. T cells and B cells normally produce antibodies which destroy or neutralise the foreign antigens (the allergens). But in people with allergy the allergens lead to an immune response which causes the damage of the local tissue or inflammation. Besides the T and B lymphocytes, the type of antibody known as IgE (Immunoglobulin E) is also responsible for causing allergic reaction and tissue damage or inflammation. The IgE antibodies cause excessive activation of special white blood cells known as mast cells and basophils.
The allergies can be divided into four different types (type 1 to IV) based on the damage that is caused to the tissue. The allergies can also be divided as acute and chronic allergy.
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