Sensitization and True Allergy

How Allergies Develop and Why Reactions Differ

Pollen
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Here is a simple fact about allergies: you cannot have an allergic reaction to a substance you've never encountered. This is because the body won’t recognize a substance as a threat until after multiple encounters.

Unlike a virus or bacteria, most allergens won’t trigger an innate response from the immune system. Rather, it’s a response that develops over time, often with no rhyme or reason as to why it occurs in some people and not in others.

The process by which your body becomes sensitive to—and allergic to—a particular substance is called sensitization.

Understanding Sensitization and True Allergies

Sensitization is a process by which the immune system will produce a defensive protein, called an antibody, in response to any substance it considers abnormal, including certain foods, pollen, mold, or medications.

The production of the antibody, however, does not necessarily lead to symptoms. Depending on the individual, the response can range from minor or nonexistent to serious and potentially life-threatening.

As such, a "true allergy" is the asymptomatic reaction triggered by the immune system in response to an allergy-causing agent (allergen). If there are antibodies but no symptomatic response, we refer to that as asymptomatic sensitivity.

Symptoms of a true allergy may include:

  • Skin rash
  • Hives
  • Itching of the eyes or skin
  • Wheezing
  • Rhinitis (nasal drip, sneezing, congestion)

In more severe hypersensitivity reactions—such as to an insect bite, a drug (like penicillin), or a food (like peanuts)—a serious form of allergy can develop known as anaphylaxis. This all-body allergic response can lead a worsening of symptoms and lead to respiratory distress, shock, and even death.

Variations in Allergic Sensitivity

Interestingly enough, allergy sensitivity not only varies by the individual but by the part of the world you live in. For example, if you reside in the southern part of the U.S., you are more likely to have an allergy to eggs, milk, shrimp, and peanuts. If you live in Italy, you are more likely to be allergic to fish.

While scientists aren’t entirely sure why this happens, some believe that the widespread consumption of certain foods within a region will naturally translate to a higher incidence of a particular allergy.

On the other hand, the way in which certain foods are processed (or even the soil they are growth) may contribute to the phenomenon. The same applies to pollutants or toxins that are prevalent in certain parts of the world and less so in others.

Ultimately, it all brings back to our central fact: you cannot have an allergy to something you are not exposed to.

Cross-Reactive Sensitivity

If a person has a true allergy, the presence of the allergic antibody will always be present in the bloodstream. As such, wherever a person is re-exposed to an allergen, the antibody will be there to trigger a response.

However, in some cases, the immune system will mistake a non-allergen for a true allergen.

This is called cross-reactivity and occurs when the protein of an allergen like pollen is similar in structure of something else, such as a fruit.

We see this sort of thing frequently with a condition known as oral allergy syndrome (OAS), a cross-reactive response between pollen and certain raw fruits.  As the primary sensitivity is to the pollen, the symptoms of allergy to the fruit tend to be milder and constrained to where the fruit came into contact with the mouth or lips.

In this regard, OAS is not a true allergy but rather a case of "mistaken identity" on the part of the immune system.

Sources:

Coleman, S. "Food allergy sensitization—new study finds geography plays a pole." Today's Dietician. 2014; 16(7): 12. 

Kashyap, R. and Kashyap, R. "Oral Allergy Syndrome: An Update for Stomatologists." Journal of Allergy. 2015; article ID 543928.

Salo, P.; Arbes, S.; Jaramillo, R. et al. "Prevalence of allergic sensitization in the United States: Results from the National Health and Nutrition Examination Survey (NHANES) 2005-2006." J Allergy Clin Immunol.  2014; 134(2):350-359.

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