As sensitivities to foods or food components become more and more prevalant, it’s important to distinguish the difference between an allergy to a food or an intolerance to a food.

A food allergy is defined as an adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food. The terms allergy and allergic disease are broadly encompassing and include clinical conditions associated with altered immunologic reactivity. An immune response is when your body develops an antibody to a food or food component. Many times, your body will produce an antibody but there are no symptoms associated with this immune response; if this is the case, you do not have an allergy. Therefore, for you to be classified as having a food allergy, both an immune response must be found plus you need to have development of specific signs and symptoms associated with the offending food.

Some symptoms of food allergies are:

• Food-induced anaphylaxis
• Immediate gastrointestinal hypersensitivity like acute immediate vomiting
• Eosinophilic inflammation of the esophagus
• Eosinophilic gastroenteritis
• Streaks of blood mixed with mucus in the stool
• Vomiting and diarrhea severe enough to cause dehydration and shock
• Oral allergy syndrome
• Itching, redness, swelling of the skin

Compare that with a food intolerance, which elicits reproducible adverse reactions but do not have established or likely immunologic mechanisms.

For example, an individual may be allergic to milk due to an immunologic response to milk protein, or intolerant of milk due to an inability to digest lactose. Thus, milk protein is an allergen that triggers an adverse immunologic reaction. Lactose induces excess fluid in the GI tract resulting in abdominal pain and diarrhea because it is not metabolized, and is therefore not an allergen.

Adverse reactions to food can therefore be best categorized as those involving immunologic or non-immunologic mechanisms as summarized below.