Food Allergy vs Food Intolerance

Overview of Food Allergy
An allergy to food involves a reaction of the immune system to a particular 
substance(s) (the allergen) present in the food that the body mistakes as 
harmful. The body then creates an antibody that recognizes the food 
allergen. The next time a person comes in contact with the same allergen, 
the body releases chemicals to protect itself. These chemicals trigger 
allergic symptoms that can affect the respiratory or cardiovascular system, 
gastrointestinal tract or skin.
Food allergies can affect adults and children, although some children may 
outgrow a food allergy. Allergic reactions can vary from person to person. 
Some are very mild and only involve one part of the body, like hives on 
the skin. Others are more severe and involve multiple parts of the body. 
Reactions can occur within a few minutes, up to a few hours or even after 
repeated contact with the food over time.

What Is Food Intolerance?
Intolerance to a food is not the same as a food allergy. Food intolerance 
is when the body has trouble digesting or absorbing a particular food 
or food component (e.g., lactose). The immune system is not involved. 
The symptoms of food intolerance can vary and usually originate in 
the gastrointestinal tract, and they can sometimes be mistaken for those of 
a food allergy.