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food allergy

Alternative Names 
food hypersensitivity

A food allergy is an immune response caused by certain foods when those foods are eaten or come into contact with the body.

What is going on in the body? 
A food allergy occurs when an immune response occurs. An immune response is a normal response of the body to something it sees as abnormal. Usually the response is to bacteria, viruses and toxins. Sometimes the body will recognise such things as foods as abnormal. When foods are recognised as abnormal, the body produces antibodies, and an immune response occurs.

Reactions can vary in strength and can range from very mild to fatal. Food allergies are not widely reported, so it is hard to know how common they are. Food allergies usually occur within 2 hours after eating and can be localised to the intestine or stomach. These allergies can also be systemic, occurring throughout the entire body.

The difference between food allergies and food intolerance is the production of antibodies and the release of histamine and other substances in the immune response. Other immune responses of the body such as asthma or eczema may be worsened by food allergies.

What are the signs and symptoms of the condition? 
Symptoms of food allergies include:
  • cough.
  • congestion.
  • wheezing.
  • shortness of breath.
  • difficulty swallowing.
  • hives.
  • light-headedness.
  • headache.
  • abdominal pain.
  • diarrhoea.
  • nausea and vomiting.
  • stomach cramps.
  • bloating.
  • itching.
  • anaphylaxis, which is a severe systemic, or total body, allergic reaction. A person will feel as if his or her throat is closing. An anaphylactic reaction is a medical emergency that warrants calling 000 immediately.
What are the causes and risks of the condition? 
Some common causes of food allergies are reactions to peanuts and peanut oil, other types of nuts, and shellfish. Other sources of food allergies are fruits such as melons, strawberries, and tomatoes, food additives, thickeners, and preservatives.

The exact number of allergies is not known. Many people think they have allergies, when they are just intolerant of certain foods. It is believed that approximately 1 percent (1%) of people have true allergies. Up to 40 percent (40%) believe that they have food allergies. Most of these are cases of food intolerance and are not food allergies.

What can be done to prevent the condition? 
There is no way to keep from developing food allergies. Once someone knows that they have a food allergy, they should avoid that food.

How is the condition diagnosed? 
A food allergy can be diagnosed by a combination of methods. A history of symptoms can reveal the allergic reactions that happen each time a certain food or additive is eaten. An examination at the time of the reaction can show wheezing and other allergic-type symptoms. Blood tests can show elevated levels of antibodies, particularly immunoglobulin E (IgE), when there is an allergy. Certain foods can cause higher IgE levels. Finally, skin tests can be done in the office of a doctor. Needles with various allergens on them are placed just under the skin and then the site is monitored for swelling. These tests try to produce the allergic reaction under the supervision of a doctor when an allergy is assumed or suspected.

What are the long-term effects of the condition? 
Some children who develop food allergies grow out of them. However, food allergies are usually lifelong conditions. Effects range from abdominal discomfort to life-threatening anaphylaxis or death. Foods that cause allergic reactions should be avoided.

What are the risks to others? 
There are no risks to others. Food allergies are not contagious.

What are the treatments for the condition? 
Treatment involves avoiding foods that cause allergic reactions. Some individuals may take medications such as corticosteroids and adrenaline during an allergic reaction. These drugs help to decrease the severity of the reaction. Antihistamines, such as diphenhydramine, may also be helpful. Some creams can help, if there is a skin rash.

What are the side effects of the treatments? 
Corticosteroids, such as prednisone, and adrenaline have a wide range of side effects. A doctor should be consulted about these medications. Antihistamines may have a drying effect and can cause sleepiness. Some of the skin creams, such as hydrocortisone can cause thinning of the skin and other side effects.

What happens after treatment for the condition? 
Most individuals who have food allergies have them for their entire lives. Some children may outgrow food allergies. In the long term, if an individual eats foods that have caused allergic reactions, an anaphylactic life-threatening reaction could result. Food allergies can lead to dietary restrictions that may cause malnutrition if the restrictions are severe. Individuals with food allergies may have an overall change in normal lifestyle and loss of some quality of life because of the inability to eat some foods.

How is the condition monitored? 
Individuals should note if they are developing symptoms when they eat certain foods. They should also note whether or not different foods are causing allergic reactions. If these occur, a doctor should be consulted.

Author: James Broomfield, MD
Reviewer: eknowhow Medical Review Panel
Editor: Dr John Hearne
Last Updated: 18/09/2004
Potential conflict of interest information for reviewers available on request

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.

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