What is a food allergy?

A food allergy occurs when your immune system reacts to specific proteins in food. It should not be confused with food intolerance, such as lactose intolerance.

Food allergies are rapidly increasing and it is not yet clear why. Research is currently focused on trying to identify factors that may be contributing to their increase and to better understand the immune reaction to food allergy.

Immune system

The organs and cells involved in protecting the body against infection.

Causes

Although allergic reactions can be triggered by any type of food, the most common are:

  • Eggs;
  • Fish;
  • Peanuts;
  • Milk;
  • Shellfish;
  • Soy;
  • Tree nuts, and;
  • Wheat.

The cause of the allergic response is the release of an antibody, called immunoglobulin E (IgE), by a type of immune cell, called a mast cell.

There are some non-IgE mediated allergic reactions, but they are not well understood. They tend to be the type associated with delayed reactions.

Antibody

A protein molecule produced by the immune system. Antibodies bind specifically to foreign substances to neutralise them or target them for destruction.

Mast cell

A type of white blood cell found in connective tissue. Mast cells play a role in allergic reactions, wound healing and immune defence.

Risk factors

Risk factors for food allergy include:

  • Family history - if you have a family history of food allergies, you are more likely to suffer from them;
  • Age - food allergies are most common in young children, although many children eventually grow out of their allergy;
  • Asthma - it is common for asthma and food allergy to occur together. People with asthma and food allergies are more likely to have severe allergic reactions;
  • Not breastfeeding - the evidence is not conclusive, but there is some evidence that suggests not being breastfed in infancy increases your risk of developing allergies later in life, and;
  • Food-dependent, exercise-induced anaphylaxis (FDEIAn) - this can occur as a result of exercising after consuming food that you are allergic to.

Signs and symptoms

The symptoms of an allergic reaction usually occur within the first two hours after consuming certain foods. Known as immediate reactions, these symptoms include:

  • Hives;
  • Wheezing;
  • A facial or generalised rash;
  • Hoarseness of the voice;
  • Stomach cramps and abdominal pain;
  • Difficulty swallowing;
  • Shortness of breath;
  • Light-headedness;
  • Itching of the mouth, throat, skin, eyes or another area;
  • Swelling of the face, lips, tongue and eyelids, and;
  • Blocked or runny nose.

Symptoms that usually occur within 1-2 days after ingesting certain foods are called delayed reactions, and include:

Child with food allergy.A food allergy can cause a rash usually within two hours of eating a certain food. 

Abdominal

Relating to the abdomen, the middle portion of the trunk which contains organs such as the intestines, stomach and liver.

Wheezing

Breathing with a whistling or rattling sound in the chest.

Methods for diagnosis

Medical history

Your doctor will ask you questions and take a detailed medical history, including family history.

Allergy testing

Skin testing

A small probe coated with a food extract is used to prick or scratch the skin, to test for a reaction. This skin-prick test is usually performed on the skin on the forearm or upper back. It is not painful and can be done on children and adults.

A negative result from a skin-prick test can be used to exclude IgE-mediated allergy.

Patch testing on skin.Skin patch testing for allergies. 

Blood tests

A number of blood tests are available to diagnose some specific allergies, but they are expensive and, unlike skin-prick testing, the results are not immediate. Their use tends to be reserved for people with skin conditions such as dermatitis or eczema.

Elimination diets

Elimination diets involve removing certain foods from your diet for a period of time and then reintroducing them in small amounts one at a time to see if symptoms develop. Elimination diets are developed in consultation under the supervision of a dietitian or allergy specialist.

Food diary

You may be asked to record everything you eat or drink in a food diary for a period of time.

Food challenges

You may be offered a supervised food challenge, in which you eat a small amount of food to which you are potentially allergic to, and your reaction is observed. If after 10-15 minutes there is no reaction, you will be given a slightly larger amount. This continues for a couple of hours and if you develop allergic symptoms, it is immediately stopped. Food challenges should only be performed with appropriate medical supervision.

Blood tests

During a blood test, blood can be drawn using a needle or by a finger prick. Your blood can then be analysed to help diagnose and monitor a wide range of health conditions.

Dermatitis

A skin inflammation that may cause redness, itchiness and swelling of the skin. There are different types of dermatitis.

Types of treatment

Adrenaline injector

If you are having an allergic reaction and experience difficulty breathing, tightness in the throat or feel light-headed, immediate treatment with an adrenaline shot or epinephrine auto-injector (commonly known as Epipen®), is usually required to prevent potentially life-threatening complications. It can also be used in children who pass out, cough or vomit repeatedly during an allergic reaction, or who have anaphylaxis (see 'Potential complications'). People with confirmed serious food allergy will often be given an adrenaline injector to carry with them at all times. It is important to seek urgent medical attention after the use of an adrenaline injector for ongoing observation. 

Immunotherapy

Immunotherapy involves the regular administration of gradually higher doses of a trigger (allergen) for a food allergy, over a period of years. Immunotherapy can be given as an injection, or as drops or tablets under the tongue. Immunotherapy changes the way the immune system reacts to the trigger, by switching off the allergy. The end result is that you become immune to the triggers, so that you can tolerate them with fewer or no symptoms.

Other therapies

Some people seek out unproven alternative therapies for their food allergy. The Australasian Society of Clinical Immunology and Allergy warns against the following techniques, which are either unproven or ineffective: cytotoxic food testing, pulse testing, reflexology, Vega testing, Alcat testing, Rinkel's intradermal skin testing, kinesiology, hair analysis and immunoglobulin G (IgG) food antibody testing.

Adrenaline

A substance secreted primarily by the adrenal glands that helps to prepare the body for exertion. It is involved in regulating blood pressure, heart rate and breathing. Adrenaline can also be used as a drug to treat a number of conditions, including cardiac arrest and anaphylaxis.

Antibody

A protein molecule produced by the immune system. Antibodies bind specifically to foreign substances to neutralise them or target them for destruction.

Immune system

The organs and cells involved in protecting the body against infection.

Potential complications

Anaphylaxis

Anaphylaxis, also called anaphylactic shock, is a severe complication of food allergy that can result in death. If you experience anaphylactic shock, prompt treatment with injectable adrenaline is vital.

Woman using epipen.Injectable adrenaline is used to treat anaphylaxis. 

Other conditions

Food allergies can exacerbate other conditions, such as asthma or eczema.

Adrenaline

A substance secreted primarily by the adrenal glands that helps to prepare the body for exertion. It is involved in regulating blood pressure, heart rate and breathing. Adrenaline can also be used as a drug to treat a number of conditions, including cardiac arrest and anaphylaxis.

Prognosis

Sometimes children outgrow allergies to milk, soy, egg and wheat if they avoid these foods when they are still young. Allergies that are more likely to be lifelong are those to shellfish, peanuts and tree nuts.

Prevention

There is some evidence to suggest that breastfeeding during infancy reduces the onset of allergies later in life. However, there is no known way to prevent the development of food allergies and if you have a food allergy, the only way to prevent it flaring up is to avoid the food that triggers it.