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Symptoms and Signs of Food Allergy

Doctor's Notes on Food Allergy

A food allergy is an adverse immune system reaction to a particular food or compound that a person eats or swallows. Signs and symptoms can begin within minutes but some take hours to develop. Common symptoms include itching, rash development, hives or wheals. Swelling of the lips and mouth may occur along with abdominal cramps, nausea, vomiting and diarrhea. Nasal stuffiness and itching of the eyes are also common. Severe signs and symptoms include difficulty breathing, swelling tongue, tightness or choking in the throat, chest tightness, rapid heartbeats, feeling dizzy and loss of consciousness – these signs and symptoms suggest the allergic reaction may be life threatening.

The cause of a food allergy is the person’s immune system overreacting to a compound (usually a protein) in the food. The majority of foods that may generate an allergic reaction are as follows: eggs, milk, peanuts, wheat, soy, treenuts, fish and shellfish. Some individuals have multiple food allergies.

Medical Author:
Medically Reviewed on 3/11/2019

Food Allergy Symptoms

A person with a food allergy can have symptoms beginning as soon as 2 minutes after eating the food, but reactions may take 1 to 2 hours to appear. Occasionally, symptoms abate quickly, only to recur in 3 to 4 hours.

  • The most common symptoms include the following:
    • Itching of the skin followed by hives, a rash of raised, reddish bumps or wheals
    • Swelling of the lips and mouth
    • Belly cramps
    • Nausea
    • Vomiting
    • Diarrhea
  • Other symptoms may include the following:
    • Itching and watering in the eyes
    • Runny or stuffy nose
  • Symptoms of a more severe reaction could include the following:
    • Shortness of breath or difficulty breathing
    • Tightness in the chest
    • Feeling of tightness or choking in the throat
    • Rapid or irregular heart beat
    • Feeling dizzy or light-headed
    • Losing consciousness
  • A severe allergic reaction can be life threatening. This severe reaction is referred to as anaphylaxis, or anaphylactic shock.
    • The dizziness, lightheadedness, and loss of consciousness are due to dangerously low blood pressure, called "shock."
    • An anaphylactic reaction can begin suddenly, or it may develop gradually with itchiness and swelling of the skin and throat and then progress to a severe reaction over a few hours.
    • Most people get such a reaction immediately after eating the food, but in a few unusual cases the reaction occurs only after exercising following the ingestion of the food.
    • Severe reactions are most often seen with allergies to nuts, fish, and shellfish, although allergy to any food can cause anaphylaxis.
    • People with asthma, childhood allergies, eczema, or prior severe food allergies are especially at risk for having an anaphylactic reaction.
  • MSG reaction can be mistaken for an allergic reaction.
    • Symptoms of MSG reaction include the following:
      • Burning sensation at the back of the neck and radiating down the arms and chest
      • Tingling and numbness in the same areas
      • Headache
      • Nausea
      • Occasionally, difficulty breathing, especially in those with poorly-controlled asthma
    • A few people experience seizures, irregular heartbeats, and anaphylaxis after the use of MSG.
    • Contrary to popular beliefs, MSG has no relation to Alzheimer disease, Huntington chorea, or other chronic illnesses.

Food Allergy Causes

An allergic reaction occurs when the body's immune system overreacts to an allergen, in this case a food protein.

  • The white blood cells produce an antibody to this allergen, called immunoglobulin E or IgE.
    • When this antibody comes in contact with the particular food protein, it promotes production and release of certain chemicals called "mediators." Histamine is an example of a mediator.
    • These mediators act on various parts of the body, mainly the skin, throat, airways, intestines, and heart.
    • The effects of the mediators on organs and other cells cause the symptoms of the allergic reaction.
  • Any food has the potential to trigger an allergic reaction, but a few foods account for most food allergies. In fact, most food allergies are triggered by one of these eight foods:
    • Eggs
    • Milk
    • Wheat
    • Soy
    • Peanuts
    • Tree nuts
    • Fish
    • Shellfish
  • Generally, people who have allergies react to only a few foods. Occasionally, a person who is allergic to one food also may be allergic to other related foods. This is called cross-reaction. Common examples:
    • Allergy to peanuts -- Cross-allergies to soybeans, green beans, and peas
    • Allergy to wheat -- Cross-allergy to rye
    • Allergy to cow's milk -- Cross-allergy to goat's milk
    • Allergy to pollen -- Cross-allergies to foods such as hazelnuts, green apples, peaches, and almonds
  • People who have a history of other allergies, such as eczema or asthma, are particularly prone to having a reaction to a food. They are also more likely to have a more severe reaction.

The Most Common Food Allergies for Kids and Adults Slideshow

The Most Common Food Allergies for Kids and Adults Slideshow

It's common to have a bad reaction to foods we eat on occasion, such as gas from eating beans or headaches from drinking wine. If you're lactose intolerant you may experience diarrhea when you consume dairy. These are all examples of food sensitivities or intolerances, which are different from allergies in that they are not immune system reactions. With a food allergy, the immune system reacts to specific foods which can result in symptoms that range from mild skin rashes or itching, to anaphylaxis, a serious reaction that can be fatal.

REFERENCE:

Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.

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