Food allergies and food intolerances are two very separate things, yet are easily confused. Knowing the differences between them determines how best to diagnose and treat them.
A true allergy involves activation of the body's immune system and usually occurs immediately after exposure to the food causing the allergy. Only 5 per cent of people have true food allergies and most of these are first seen during childhood.
Natural foods such as peanuts, milk, eggs, soy and shellfish are by far the most common cause of food allergies. An allergic reaction to one of these foods usually involves eczema or hives and in very sensitive people can lead to anaphylaxis  - a potentially life-threatening condition.
For someone with a food allergy (which would normally be first seen in childhood), the best advice is to avoid the offending food, seek professional advice about appropriate substitutes and be prepared for emergency treatment in the event of a severe flair-up or anaphylaxis. Many children outgrow food allergies, especially if the allergy started before age three; however, some allergies, like those to nuts and fish, are unlikely to disappear.
Diagnosing of an allergy involves a combination of tests. One method is a skin prick test where a small amount of the suspected allergic substance (allergen) is placed on the arm and the skin is pricked to allow the allergen to enter just below the skin surface. Within about 10 minutes a small itchy wheal will appear if there is an immune response to the allergen.
Another type of allergy testing is done by a blood test which measures IgE (immunoglobulin E). IgE is at the frontline of the body’s immune response to allergenic substances. By using a combination of skin prick and blood tests it is possible to work out if the allergy is from a food or from common environmental factors such as pollens, dust mites, dog or cat fur.
Food intolerances are much more common than food allergies, though much harder to identify. Signs of the intolerance may need several days of exposure to the food substance before symptoms are seen; making it very hard to identify what is causing the problem. Food intolerances can occur at any age and typically affect behaviour, gastrointestinal function (colic, reflux or changed bowel habits) or result in rashes.
Typical food chemicals that can cause problems are salicylates, amines and glutamate. Salicylates are naturally found in fruits, vegetables, yeast extracts and honey and are present in some flavourings, perfumes, scented toiletries and aspirin. Amines are naturally found in cheese, chocolate, yeast extract, fish, bananas, tomatoes and broadbeans. Glutamate is found naturally in tomatoes, cheeses, mushrooms and stock cubes although is also found added to food as monosodium glutamate (MSG; designated as additive number 621 on a food label).
Lactose intolerance is one example of a food intolerance. A person with lactose intolerance lacks an enzyme (lactase) that is needed to digest milk sugar. When the person eats milk products, symptoms such as gas, bloating, and abdominal pain may occur.
Food intolerances can only be identified by following an appropriate elimination diet and challenge protocol under the direction of an appropriately qualified professional. Because intolerances do not involve the immune system, skin prick and blood tests are not able to identify the problem. Once an intolerance to a substance has been identified, then avoidance by knowing what foods contain the substance is the best idea.
Where to go for more information
- Allergy & Anaphylaxis Australia www.allergyfacts.org.au 
- The Australasian Society of Clinical Immunology and Allergy www.allergy.org.au 
Confused about the mixed soup of nutrition messages being stirred through the media? Tim maintains an active nutrition blog at www.thinkingnutrition.com.au  where you'll find the latest nutrition research and controversies discussed in straight forward language, distilling out what you need to know for your better health