Food allergies are an over response by the immune system in which allergy antibody (known as IgE) is produced against the offending food.  With further exposures, the IgE reacts with cells in the body and an allergic reaction is triggered.  Most food reactions are very obvious, with the onset of symptoms within minutes of exposure.  Some food reactions may be delayed and begin several hours later, making the diagnosis more difficult.  The reactions may range from the very mild (a facial rash and itchy mouth) to severe life threatening anaphylaxis.  Severe food reactions may be fatal.

Signs and Symptoms of an allergic food reaction:

  • skin:  hives, redness, swelling, facial rash
  • airway: tightness in the chest/throat, gagging, coughing, wheezing, shortness of breath
  • gastrointestinal: itchy tongue/mouth, vomiting, stomach pain
  • cardiovascular: fainting, lethargy, shock   
  • general: itchy palms/feet, feeling a sense of doom

It is true that food allergies are on the rise. Peanut allergy has doubled in the past 10 years and research has not been able to provide a single good explanation for this increase. Food allergies vary based on age and geographic location.  For instance, while peanut allergy is common in the United States, it is rare in China where rice allergy is much more frequent.

Although allergies may occur to any of hundreds of foods, over 90 % of food allergies are caused by only 10 foods.  In children, the 5 most common food allergies are: egg, milk, peanut, soy and wheat.  Most children will outgrow egg and milk allergy while peanut allergy tends to be lifelong.  For adults, the common food allergies are to shellfish, fin fish, tree nuts, and peanuts.  In some children, the initial sign of a food allergy may be a refusal to eat a common food such as egg or peanut.  The parent may mistake this for a texture or a preference issue but, in fact, this is a common way for a young, nonverbal child to display an allergy.

Food Intolerance refers to reactions to foods which are not caused by IgE antibody.  These reactions are not life threatening but can still be very uncomfortable and problematic.  Many people use the term ‘food allergy’ for these reactions which leads to lots of confusion.  The most common food intolerance is gastrointestinal upset such as bloating, diarrhea, stomach pain and gas due to milk and lactose intolerance or wheat and gluten intolerance.  In some cases we know the mechanism of intolerance to foods: milk/dairy-deficiency of digestive enzymes for lactose (milk sugar); gluten-non allergic immune reaction to grain protein. Other food reactions like heartburn after eating spicy foods, gas after eating beans, anxiousness after ingesting caffeine or chocolate are common and vary from person to person.

Allergy tests are not helpful for food intolerances, even when the reaction is severe.

In addition to classic immediate food reactions, there are other conditions associated with food allergies for which allergy testing can be helpful:

  • food dependent exercise induced anaphylaxis
  • oral allergy syndrome, itching limited to the mouth and throat after eating fresh fruits and vegetables
  • eosinophilic esophagitis-indigestion and swallowing disorders
  • atopic dermatitis (eczema)

Though food reactions can affect health in many ways, IgE reactions are not felt to play a significant role in the following conditions and food allergy testing is not indicated or helpful:

  • headaches, migraines
  • fibromyalgia, psoriasis
  • rheumatoid arthritis
  • autism, ADD
  • lactose intolerance
  • gluten intolerance
  • bloating, diarrhea , stomach pain
  • irritable bowel syndrome