Food allergy

Many people will have an unpleasant reaction to something they eat or drink, and think they may have a food allergy. However, most of these people are more likely to have what’s called a ‘food intolerance’, rather than a true food allergy. Proven food allergies occur in approximately one in 20 children and about one in 100 adults.

Both a food allergy and a food intolerance can make you unwell, but a food allergy has the potential to be life-threatening.

Differences between food allergy and food intolerance
Food allergyFood intolerance
Involves the immune system.Does not involve the immune system.
Symptoms include rash, hives, vomiting, diarrhoea, abdominal cramps and occasionally difficulty breathing.Can cause abdominal pain, wind, diarrhoea, headache, mouth ulcers, hives and runny nose.
Symptoms usually appear a few minutes to an hour after eating the food.Symptoms can appear within minutes of eating the food or more usually several hours, but can take several days to appear.
Food allergy can be mild or severe and in extreme cases can cause life-threatening anaphylaxis. 
Examples of food allergy are allergies to nuts, fish, shellfish, eggs and sesame seeds.Food chemicals or additives (such as flavours or preservatives) are often the cause of food intolerances.

Food allergy

A food allergy involves a reaction of your immune system, whereas a food intolerance does not. If you have a food allergy your immune system makes antibodies against a particular (normally harmless) food. It’s as if your immune system mistakes that type of food for a harmful foreign invader. This means that when you eat the particular food again, the pre-formed antibodies swing into action and trigger a cascade of reactions in your tissues that result in some or all of the typical symptoms of food allergy:

  • mouth itching and swelling;
  • rash;
  • hives;
  • runny nose;
  • vomiting;
  • abdominal pain;
  • diarrhoea;
  • swelling of the throat and tongue; and
  • sometimes difficulty breathing.

These symptoms usually occur within 30 minutes of eating the food.

There is also a delayed type of food allergy that causes symptoms (often affecting the skin or digestion) 24–72 hours after eating a food that you are allergic to. This type of allergy is not well understood and can be difficult to diagnose.

Anaphylaxis: a medical emergency

Food allergy symptoms are often severe, and sometimes life-threatening. A severe, sudden, life-threatening allergic reaction is called anaphylaxis. Anaphylaxis is a medical emergency that needs immediate treatment. Symptoms of anaphylaxis include:

  • swelling of the lips and tongue;
  • difficulty breathing;
  • widespread rash;
  • vomiting;
  • wheeze;
  • sudden drop in blood pressure; and
  • collapse.

Common food allergies

The foods most commonly associated with food allergy are:

  • milk;
  • eggs;
  • nuts, especially peanuts;
  • grains, such as wheat, oats and rye;
  • soy;
  • fish and shellfish;
  • sesame;
  • tomatoes, berries and other fruit.

The allergic reaction is usually to a protein within the food.

Most children who have an allergy to soy, wheat, milk or eggs grow out of this by the time they start school, whereas an allergy to seafood or nuts is likely to be severe and last for life.

Diagnosis of food allergy

See your doctor for diagnosis of food allergy. You will be asked to describe your symptoms, and your doctor may suggest blood tests or skin prick tests to investigate whether you have a food allergy. You may be referred to an allergy specialist for these and possibly other tests. It is important to know exactly which food is causing your allergy so that you can avoid it in the future.

Treatment of food allergy

The treatment for food allergy is to completely avoid the food that causes your allergy. People who have a severe allergy should be careful to avoid even touching the food or eating trace amounts of it, which may be present in processed foods. A dietitian can show you how to recognise the relevant ingredient on food labels.

If you are thought to be at risk of a severe allergic reaction to a food, your doctor or specialist may advise you to wear an identifying bracelet such as a MedicAlert bracelet and possibly to avoid certain medicines. He or she should also give you a written ‘Anaphylaxis Action Plan’ telling you what to do in the event of a severe allergic reaction.

Adrenaline self-injection devices (auto-injectors)

As part of your Anaphylaxis Action Plan, your doctor or specialist may advise that you carry with you at all times an adrenaline self-injection device such as an EpiPen or Anapen. The medicine in the adrenaline auto-injector helps treat severe allergic reactions by shrinking blood vessels that have become too expanded, making your heart beat more strongly and helping you breathe.

Your doctor or specialist should explain when and how to use the adrenaline auto-injector. You can practise with a training device that has no needle or medicine so that you know what to do with the real device should the need arise.

If you develop signs and symptoms of a severe allergic reaction as described by your doctor or pharmacist, inject the adrenaline into your thigh muscle straight away as you have been shown, and seek urgent medical help.

Children may be prescribed either a regular or reduced-dose auto-injector, depending on the severity of their allergic reactions and their body weight.

Check your device regularly and take it to your pharmacist for a replacement if it is approaching or past its expiry date or if the packaging gets damaged.

What is food intolerance?

Food intolerance is an abnormal response to a food (often to a ‘food chemical’ or additive), resulting in symptoms of illness. Food intolerance is not an immune system reaction and does not generally cause life-threatening symptoms. The suspect food chemical may occur naturally in the food or it may be added to foods to enhance their flavour or preserve them.

A food intolerance can mean you have symptoms to a range of foods because the suspect chemical may be present in many different foods. In contrast, a person with a food allergy will often react to only one or 2 foods.

Food intolerance is a more common condition than food allergy and may cause diarrhoea, nausea, cramping or headache soon after eating the food, hours later, or even days after eating the food. The severity of symptoms can vary because the suspect food chemical can accumulate in the body, depending on how much of the suspect food (or foods that contain the suspect chemical) you have eaten. Eating a small amount of the suspect food may not cause symptoms, but eating a lot of it can.

Sometimes a food intolerance occurs when your body is not able to process a food component. A good example of this is lactose intolerance where the person lacks the enzyme necessary to break down the milk sugar (lactose) for proper digestion.

Food intolerance won’t show up in the blood tests or skin prick tests used to diagnose food allergy. The symptoms of food intolerance are often similar to the symptoms of food allergy and many other conditions. To find out if you have a food intolerance, your doctor may refer you to a dietitian, who will supervise eliminating and reintroducing various foods in your diet, one at a time, to check the effect on your symptoms. You should not carry out an elimination diet without supervision by your doctor or specialist or a dietitian.

The treatment for a food intolerance is usually to avoid eating large amounts of foods that contain the suspect food chemical, so that the chemical does not accumulate in the body and so you can prevent symptoms from appearing. A dietitian can help you devise an eating plan that helps you achieve this, yet still allows you to enjoy a balanced diet that includes all the essential nutrients.

Last Reviewed: 1 August 2012
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References

1. Australasian Society of Clinical Immunology and Allergy (ASCIA). Food allergy (updated January 2010). http://www.allergy.org.au/patients/food-allergy/food-allergy (accessed Aug 2012).
2. Australasian Society of Clinical Immunology and Allergy (ASCIA). Management of food allergy http://www.allergy.org.au/patients/food-allergy/management-of-food-allergy (accessed Aug 2012).
3. Australian Resuscitation Council. Guideline 9.2.7 Anaphylaxis – first aid management; July 2012. http://www.resus.org.au/policy/guidelines/section_9/anaphylaxis_first_aid_management.htm (accessed Aug 2012).
4. Australasian Society of Clinical Immunology and Allergy (ASCIA). Food intolerance (updated January 2010). http://www.allergy.org.au/patients/food-other-adverse-reactions/food-intolerance (accessed Aug 2012).
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