Food allergies are a growing problem around the world []. These days, if you do not personally suffer from an allergy, you almost certainly know someone who does. Currently, around 3-7% of children have a food allergy—about a 50% increase since 1997 [1, 2]. For many people, allergies are little more than a nuisance, but for others, an allergic reaction can be life threatening.

What is a Food Allergy? 

The term “allergy” is often used fairly loosely to describe any adverse reaction to a food. A true allergy, however, is unique in that it is caused by the immune system reacting to a specific protein – an allergen – as if that protein were a threat to the body. Food intolerances are often confused with food allergies, since many of the symptoms of a food intolerance are similar to those caused by an allergic reaction. However, a food intolerance usually results from the inability to digest certain substances due to enzyme defects [], not an immune reaction. For instance, lactose intolerance results when an individual does not have sufficient levels of lactase. Lactase is an enzyme required for the digestion of lactose, a sugar found in milk products []. In the case of lactose intolerance, the symptoms may be similar to those of a milk allergy, but the immune system is not involved.

What Causes an Allergic Reaction?

If you suffer from an allergy, you can blame it on two main culprits: mast cells, which are cells located throughout the body that are involved in normal immune responses [], and a special type of antibody, called IgE. Antibodies are Y-shaped proteins produced by cells in the immune system that recognize proteins on pathogens or other harmful foreign substances invading the body in order to disarm them or target them for destruction by other components of the immune system []. The antibody recognizes a certain protein or part of a protein on the foreign object and attaches to the object. IgE antibodies are one of five types of antibodies, all of which have different roles in immune response. The main function of IgE antibodies appears to be to defend the body against parasites, such as the parasite that causes malaria [].

No one has a reaction the first time they encounter an allergen. Instead, when a person first meets an allergen, the body makes lots of IgE antibodies that recognize a protein on the allergen []. Then the “stem” side of the newly made Y-shaped antibodies attaches to a mast cell. The next time the person comes in contact with the same allergen, these IgE proteins immediately recognize it and signal to the mast cells to release several chemicals, histamine in particular, that are involved in the inflammatory response []. These chemicals increase blood flow, allow the spaces between cells to fill with fluid, and cause local nerve endings to signal pain []. When the immune system is responding to a pathogen, increased blood flow is critical for allowing white blood cells in and out of the site of infection, and fluid secretion is important for ridding the body of the intruder. This is great when your body is really under attack by a parasite, bacteria or a virus. However, the release of these chemicals in response to a harmless substance results in the host of symptoms we see during an allergic reaction, such as swelling, itching, coughing/sneezing, rash, runny nose, diarrhea and vomiting [] (see figure).

What Treatments Are Available For Allergies?

There is no cure for allergies, although immunotherapy, which involves gradually exposing people with an allergy to increasing quantities of the allergen, may be effective at decreasing patient sensitivity to the allergen []. However, most often, people use other allergy treatments. Anti-histamines, such as Claritin, Allegra, and Benadryl are often taken to block histamine, thus lessening the symptoms that arise from the release of histamine []. Those with serious allergies often carry an EpiPen []. The “Epi” stands for epinephrine, which is better known as adrenaline. Epinephrine is released naturally by your body when you sense danger, but it can help during an allergic reaction by constricting blood vessels to clear airway obstruction and decreasing the release of inflammatory chemicals like histamine [].

What Makes an Allergen an Allergen?

 All proteins have the potential to be allergens, but in reality, only a small percentage of proteins cause allergic reactions. In fact, up to 90% of allergic reactions to food are caused by proteins in only eight foods: milk, peanuts, tree nuts, shellfish, soy, wheat, fish, and eggs. Unfortunately, scientists don’t know why some proteins are more likely to cause an allergic reaction []. Even when researchers looked at the structures of common allergenic proteins, they weren’t able to find any similarities [].  One possibility is that allergenic proteins may be more likely to form clusters of two or more of the same protein, and it is this aggregation that tells the body to attack []. On the other hand, researchers do know that many allergenic foods contain more than one allergenic protein. For instance, soy actually contains 15 allergenic proteins, which may help explain why soy is a very commonly identified allergen [].

The question of what makes a protein allergenic is just one of many that researchers are investigating. Researchers are also trying to determine why some people differ in their susceptibility to allergies and why allergic reactions vary in their severity. Scientists do know that allergies are often passed down from your parents. Additionally, if a person is exposed more frequently to an allergen, the reaction tends to be less severe []. Scientists also have a few ideas as to why allergy cases are rising, but much research remains to be done to answer this question. The ability to predict what proteins will be allergenic and who might be most susceptible would be especially useful in drug development and the creation of genetically modified foods. More critically, understanding why allergy rates are increasing might allow us to make adjustments in our lifestyles in order to prevent the development of allergies in future generations.

Hannah Foster is a PhD candidate in the Molecules, Cells, and Organisms program at Harvard University


1. Wilson, J. Childhood food, skin allergies on the rise. (2 May 2013). CNN <> [26 Feb 2014]

2. Food Allergy and Food Intolerance. European Food Information Council. <> [26 Feb 2014]

3. Food allergens of plant origin – the relationship between allergenic potential and biological activity. Protall Project. <>

4. How mast cells work. Allergic and Immunologic Disorders. (19 Apr 2005). < >[26 Feb 2014]

5. Landau, E. New treatment may offer hope for peanut allergy. CNN. (31 Jan 2014) < >[26 Feb 2014]

6. Allergy Medications. WebMD. [10 Mar 2014]

7. Management of Anaphylaxis. EpiPen. <> [26 Feb 2014]

8. Aalberse, RC. Structural biology of allergens. 2000. Journal of Allergy and Clinical Immunology. 106(2):228-38.

9. Untersmayr, E. and E. Jensen-Jarolim. 2006. Pharmacology & Therapeutics. 112:787-798.

10. Allergies: What’s Behind Them? GMO Compass. (10 Jan 2006). <> [25 Feb 2014]

11. Lundgren, L. “What Makes Some People Susceptible to Allergies?” How Stuff Works. [10 Mar 2014]

Links of Interest

Description of the mechanism underlying an allergic reaction:

If you think your allergies make life difficult, watch this video of 10 unusual allergies:

One thought on “When Good Immune Systems Go Bad

  1. Most of the allergies seem to happen to the processed food and not natural raw materials/vegetables/food products.

    Example 1, My wife was perfectly fine with raw milk that we heated at home but once we moved here to US she developed allergies to processed milk (like 2% fat milk and all). She still is fine with organic milk which does not give her problems.

    Example 2, My niece is allergic to processed peanuts but not raw natural peanuts. It does not matter which brand we use.

    I have had lots of such stories within my sphere of influence where they are allergic to prepacked, processed food and once they switch to cooking food at home from scratch with raw veges and all all their allergies disappear.

    The point that I am trying to make here is that this high increase in food allergies that we see may quite likely be a manifestation of how we process our food and what other proteins or non-natural products we are injecting along with our food which our body (perhaps rightfully) recognizes as foreign and unnatural.

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