What is the difference between allergy and intolerance?

They are different : Allergy is an altered response by your immune system to an allergen. Allergens are usually harmless particles like pollens, dust, cat dander or even certain foods, wherein your body has antibodies that fight them releasing chemicals to get rid of them. Intolerance is where your body is not able to process certain proteins like milk protein or gluten. One good example would be lactose intolerance.

Complicated: An allergy is an immune response. There are many patients who have non-allergic rhinitis symptoms which can mimic allergy but are triggered by irritants such as odors, weather changes, viruses or dust irritants.

Totally different: An allergy results in a complex process in which subtypes of wbcs called eosinophils, mast cells, & basophils may be activated. This may lead to release of histamine (hence anti-histamine drugs). But you will get an increase in ige (a type of antibody) that triggers chemical release from these cells. Intolerance is a bad reaction to something (like vomiting). No ige or histamine release occurs.

The immune response: An allergy is caused by specific cells and/or proteins in the body that are designed to recognize specific sites in the allergen, i.e. Peanut, walnut, cat dander, etc. These include immunoglobulin e, and t and b cells. An intolerance is caused by an inability to digest a sugar or protein, but does not involve the same immunoglobulins and cells.