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What Happens During a Food Reaction?

When an allergic person is exposed to her/his food ALLERGEN (the specific substance that s/he is allergic to), s/he may develop an allergic reaction. The reaction is an “overreactivity” called a HYPERSENSITIVITY REACTION.  This is when the immune system mistakes what should be a harmless substance as a potential foreign invader. Since our immune systems are responsible for protecting us, it gets activated upon seeing even microscopic amounts of the allergen, and starts a cascade of immune reactions in an attempt to protect us and tries to get rid of and remove the substance from our bodies.


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Cells, proteins, and chemicals (that are stored in the body’s cells) are always present in our bodies to protect us.  The body is able to rapidly mobilize these agents, during a perceived threat.  When allergens are detected, the chemicals (stored primarily in MAST CELLS and BASOPHILS) are released, including HISTAMINE, LEUKOTRIENES, PROSTAGLANDINS, TRYPTASE, and CHYMASE).  Chemicals attract other white cells such as EOSINOPHILS to the area.

The body’s defense systems result in reactions like skin redness, itching, swelling and rashes, itchy eyes, runny or stuffy nose, upset stomach and vomiting, trouble breathing or swallowing, light-headedness, chest pain and uneven heartbeat.  To review additional signs and symptoms, click on the article on Signs and Symptoms of Allergic Reactions.

How bad can allergic reactions get?

Doctors who treat reactions think of spread (local or systemic) and severity (mild, moderate, or severe) when we think about what treatment a person needs.  A systemic reaction is known as ANAPHYLAXIS.  

Reactions that are limited to a certain region of the body are not considered systemic but may be quite severe and uncomfortable or even life-threatening. An example of a mild local reaction would be mild lip and mouth itching after taking bites from an apple.  An example of a severe local reaction would be closing of the throat after accidentally ingesting peanut, which may lead to asphyxiation.

By the same token, someone may experience anaphylaxis that can range from mild to severe as well. A mild systemic reaction may occur for example after ingestion of small quantities of food during an oral food challenge at the doctor’s office, which may be manifested as a few hives, feeling hot and flushed, and having nasal congestion developing 15 minutes after a challenge dose.  Systemic reactions, and even local reactions that become worse and progress, may result in low blood pressure and breathing difficulties that can lead to fatality.

The severity of the allergic reaction may vary with the following factors:

  • the quantity of allergen ingested
  • the way and location that allergens enter the body
  • how long the allergen stays around or how quickly it gets absorbed
  • how sensitive a person is
  • Underlying health issues and medications taken for each person
  • How many allergens are ingested (for those with multiple allergies)
  • What other allergic conditions the person has and if they are controlled

In addition, there are several situations that may make an allergic reaction more pronounced, more severe, more likely:

  • Exercise or over-exertion
  • Increased internal body temperature and heart rate (which result in the skin getting warm and hot as well)
  • Alcoholic beverages
  • Exercise
  • Menstrual cycle changes
  • Emotional stress
  • Certain medications
  • Fasting or being dehydrated

Being cognizant of triggering factors, quickly recognizing an allergic reaction, and immediately treating it to minimize progression are the best ways to gain control and prevent potential fatalities.

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