Allergy vs Sensitivity

On May 12th,  I was interviewed on CJAD radio in Montreal on the Tommy Schnurmacher show.  The topic was the effect of the polluted environment on health and why women are more afflicted with environmentally related illnesses than men. There was a phone in segment for people to call in questions.  The last caller was scornful. He told me that he had allergies during childhood, had received allergy shots, was no longer allergic, and insisted that he would continue to use deodorant. I could only respond to the latter point, that it was his personal choice to apply chemicals to his body, because we had run out of program time.

I’m using this post to elaborate on this issue because it is really important for people to understand that there are significant differences between allergy, which can respond to allergy shots, as described by the caller, and sensitivities to chemical substances or foods. But, his confusion is not surprising. There has been a tendency during the last couple of decades to use the word “allergy” to describe all kinds of unexpected reactions to substances that are tolerated by most people. To add to the confusion, allergists have had great difficulty to precisely define allergy as well.

Definition of allergy

The term allergy was developed in 1906 by Clemens von Pirquet from a combination of two Greek words, allos, meaning “other,’ and ergon, meaning “reaction”.  He created the foundation for the modern science of immunology by appreciating that a foreign substance can sensitize: that it can cause an animal to produce a different response to a substance after subsequent exposures.  He coined the word allergy to describe sensitization.  But what he was describing was the phenomenon of being programmed by an invading organism, in this case it was tuberculosis. He understood that the body was being transformed into a state of increased preparedness; it was trained to defend itself.

Unfortunately, with the passage of time, the word allergy evolved and is now used to describe only the pathological sensitization to foreign substances, which are ordinarily harmless.  It has become restricted to a limited group of conditions such as hay fever, hives, allergic asthma, allergy to stinging insects, and food anaphylaxis.  An allergic reaction is an abnormal immune system response to normally harmless environmental substances.  The reactions can cause nuisance symptoms, such as itching, or potentially life-threatening responses, such as asthma or anaphylaxis.  These reactions are triggered by harmless everyday substances such as pollen, dust, food, and animal danders, or perhaps venom from insect stings, such as wasps or bees.

These disorders almost always involve one immunological response, caused by an antibody called immunoglobulin E, or IgE, which the modern-day skin prick test used by allergists is very accurate in detecting. Or, it can just involve sensitized cells of the immune system.


Sensitivities also fall under the term that Pirquet developed.  They are “other” “reactions” too. But, there is no test like the skin prick test for sensitivities. They can develop at any time during someone’s lifetime and symptoms can be delayed which makes a diagnosis difficult to make.  For example, gluten sensitivity is diagnosed by a blood test for antibodies to gluten, which are not IgE.  Symptoms can include abdominal pain, bloating, aches and pains, diarrhea, abdominal cramps, fatigue, headaches, and rash.

Sensitivities or intolerances affect many people and can develop at any time of life.  Because the symptoms may not be as obvious, it can be difficult to find the culprit.  Symptoms of food sensitivities also involve the immune system and include:  gastrointestinal complaints of nausea, heartburn, abdominal bloating, flatulence and diarrhea, headaches, and muscle and joint pain. Sensitivity to chemical pollutantssuch a scented products primarily involve the nervous system and provoke headaches, fatigue and changes in cogntion. But, they can also invoke immune system responses such as runny nose, asthma and rash.


The caller on the radio show shared that he had been treated with allergy shots and his allergies improved.  The only treatment for sensitivities at this time is avoidance.

When a culprit is a food, avoidance is easy because someone can choose to eat an offending food or not.  When a culprit is a scent, such as scented deodorant, and the person wearing it is in the vicinity of someone who is sensitive, they can be the cause of a debilitating reaction which is why so many hospitals, public buildings, and businesses are bringing in scent free policies.  Our caller should at least restrict his deodorant choices to those which are scent free.

To hear the interview on CJAD radio, click here.

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