What is a 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. Only about 1.5 per cent of adults and 6 per cent of young children have proven food allergies.
Both a food allergy and a food intolerance can make you unwell, but a food allergy has the potential to be life-threatening.
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 (essentially 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
- sometimes difficulty breathing.
These symptoms usually occur a few minutes to 2 hours after eating the food.
Anaphylaxis: a medical emergency
Food allergy symptoms are often severe, and sometimes life-threatening. A severe, sudden, life-threatening 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
- 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.
Finding out if you have a food allergy
See your doctor for diagnosis of food allergy. Combined with a description of your symptoms, your doctor may suggest blood tests or skin prick tests to confirm a food allergy. You may be referred to an allergy specialist for these tests. It is important to know exactly what food is causing your allergy so 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 at risk of a severe allergic reaction to a food, carry with you at all times 2 adrenaline self-injection devices called EpiPens. If you accidentally eat or come in contact with the food, inject the first EpiPen into the thigh muscle straight away, and seek urgent medical help. Give the second EpiPen 10 minutes later, if needed.
Check your EpiPen 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. It is not an immune system reaction. The suspect food chemical may be naturally occurring in the food or it may be added to foods to enhance the flavour or preserve the food.
A food intolerance can mean you have symptoms to a range of foods because the suspect chemical may be present in many different foods. Compare this to a person with a food allergy, in which case they often only react to just one or two 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 you don't get an accumulation of the chemical in the body and 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.
