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Common Food Allergies & How to Spot Them

While some of us have these severe deadly reactions to our food allergies, some have a food allergy that shows up in a milder, less immediately dangerous form. Our immune system quietly reacts to foods, often without our even realizing it.


Food allergies are not all created equal. Most people know if they are severely allergic to a food – their throat closes up, their lips and/or eyes begin to swell, and it becomes increasingly difficult to breathe.  This type of food allergy can be deadly, and great care is necessary to avoid very serious consequences. Carrying an epi-pen just in case exposure does happen is a good idea for individuals who have this type of severe reaction to foods.
The 7 most common food allergens are:

Tree Nut
Cow’s Milk

There are Two Different Reactions to Food Allergens

While some of us have these severe deadly reactions to our food allergies, also known as Anaphylaxis Type 1, or Immediate Hypersensitivity Reactions—some of us have a food allergy that shows up in a milder, less immediately dangerous form. Our immune system quietly reacts to foods, often without our even realizing it.

This quiet, more subdued reaction to common food allergens like peanut, seafood, tree nut, cow’s milk, egg, soy and wheat can cause different symptoms as well.

What is an allergic reaction to food?

An immune reaction is simply a form of attack by white blood cells and results in inflammation, which is triggered by a food allergen. Instead of attacking a bacteria or other foreign invader, the immune system will attack a food particle that causes the allergic reaction.  White blood cells will secrete inflammatory chemicals, and the body experiences a small amount of inflammation after each exposure to a food allergen.

The difference between Anaphylaxis and this quiet inflammation response? They are both sparked by exposure to a food allergen. They are both triggered by immune cells. The difference between anaphylaxis and a quiet immune response is the type of proteins immune cells release following exposure to a food allergen.

Scientists have names for different kinds of white blood cell reactions, based upon which protein –or immunoglobulin—they produce in a reaction to a food allergen. Anaphylaxis Type 1 – an immediate hypersensitivity reaction, results in your immune cells secreting immunoglobulin G—or IgG in addition to immunoglobulin M—or IgM. This combination produces a nearly immediate and quite severe reaction when an individual is exposed to their food allergen. Often, people report tingling or itching in the mouth, hives, itching or eczema, swelling of the lips, face, tongue and throat or other parts of the body, wheezing, nasal congestion or trouble breathing, abdominal pain, diarrhea, nausea or vomiting, dizziness, lightheadedness and/or fainting. These are all symptoms of a severe food allergy reaction, and require immediate medical attention, especially if there is a sudden drop in blood pressure. In this situation, you want to call 911 immediately.

On the other hand, minor food sensitivity reactions may cause ‘hidden’ symptoms by increased underlying inflammation in the body.  Minor food sensitivity reactions elicit a different response from white blood cells, and instead of secreting the immunoglobulins IgG + IgM, instead they produce IgG + IgE. This causes a very different result in the body, and is typically not as dangerous as anaphylaxis. But it can still cause some irritating symptoms when you consume an offending food daily.  Some of the symptoms of a minor food allergy—also called food intolerance—include stomach discomfort, nausea, diarrhea, gas, cramps, bloating, heartburn, headaches, fatigue, and irritability or nervousness.

Best Way to Test for Food Allergies

The only way to determine a true food allergy is to have a blood test performed to test for it. The laboratory can test your white blood cells’ reaction when exposed to a small amount of a potentially offending food. They can determine if it involves an IgG, IgM, or IgE response. If your white blood cell has a reaction when exposed to cow’s milk, for example, then you would test positive for that food allergy. Even if your throat doesn’t close up – you still have an allergy to cow’s milk because your body reacted.

A common food intolerance is lactose intolerance, but this is not a true food allergy, because your immune system is not recruited – you simply do not have the digestive enzyme to break down the sugar – or lactose—found in milk. The bacteria in your colon end up breaking it down instead, which often causes the uncomfortable digestive symptoms in people who are lactose intolerant. But there is not an immune response, so lactose intolerance is not a true food allergy.


Janeway CA Jr, Travers P, Walport M, et al. Immunobiology: The Immune System in Health and Disease. 5th edition. New York: Garland Science; 2001. Effector mechanisms in allergic reactions. Available from:

Centre for Clinical Practice at NICE (UK). Food Allergy in Children and Young People: Diagnosis and Assessment of Food Allergy in Children and Young People in Primary Care and Community Settings. London: National Institute for Health and Clinical Excellence (UK); 2011 Feb. (NICE Clinical Guidelines, No. 116.) Appendix 3.1, IgE-mediated food allergy – Cost effectiveness analysis. Available from:

Written By Sydney Lappe, MS, RDN. Published on August 28, 2015. Updated on August 28, 2015.


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