What Is Sensitization?

You can't have an allergic reaction to a substance you've never encountered. In many cases, it takes multiple encounters before an allergic reaction is evident. The process by which your body becomes sensitive to -- and allergic to -- a particular substance is called sensitization.

What Does Sensitization Mean?

Sensitization is the production of a specific type of allergic antibody by the immune system resulting in a positive allergy test, such as to a particular food or pollen.

The production of the the antibody, however, does not necessarily lead to an allergic reaction. It is possible for a person to make a specific allergic antibody to a food, for example, without experiencing allergic reactions when that food is eaten.

The journal Today's Dietician explains the prevalence of false positive results to tests for allergies:

Skin prick tests and serum blood tests check for IgE antibodies to specific proteins. Positive tests indicate that sensitization has occurred. The more drastic the positive result, as evidenced by a larger wheal size (the large red bump that appears at the site of the skin prick) or higher numbers of IgE antibodies in the blood, the more likely an individual has a true allergy. However, it’s important to recognize that false-positives are common, occurring in up to 60% of blood tests and skin prick tests.

Because it is possible to be sensitized without having symptoms, it may be necessary to follow up with additional tests such a oral food trials to determine which foods to stay away from.

Who Is Sensitive to What?

Interestingly, people in different areas are more likely to be sensitive to different foods. For example, if you live in the southern part of the United States you're more likely to have allergies to eggs, cows milk, shrimp, and peanuts. If you live in Italy, however, you're more likely to be allergic to fish.

Researchers don't have a definite answer to the question about why people in particular areas are more sensitive to certain foods. The most obvious reason is simply that people in the United States, for example, are more likely to eat peanuts while Italians are more likely to eat fish. Exposure to these foods is essential for sensitization.

Another possible reason for these differences may lie in environmental exposure to environmental factors. For example, exposure to certain pollutants seems to be a factor in some cases of asthma -- though some people can experience those pollutants with no allergic response.

It is helpful to know that a person who is sensitized to one particular allergen is more likely to also be allergic to related allergens. People with peanut allergies, for example, are more likely to be sensitized and allergic to tree nuts, and people with allergies to dust mites are more likely to be allergic to shrimp. Dog allergies often translate into related cat allergies.

Resources:

Blood tests. Food Allergy Research & Education website. http://www.foodallergy.org/diagnosis-and-testing/blood-tests

Coleman, S. Food allergy sensitization—new study finds geography plays a pole." Today's Dietician. July, 2014, Vol. 16 No. 7 P. 12. 

Salo PM, Arbes SJ, Jaramillo R, et al. Prevalence of allergic sensitization in the United States: Results from the National Health and Nutrition Examination Survey (NHANES) 2005-2006 [published online February 9, 2014]. J Allergy Clin Immunol. 

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