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Step-by-step food allergy diagnosis

Food allergies are on the rise, for reasons not fully understood. Allergy Today editor Paulette Crowley explains the path to diagnosis if you suspect food allergy.

A food allergy happens when your immune system responds to the food you eat as a foreign body, and attacks it by releasing histamine.

Around one in 20 people will develop a food allergy at some point in their lives, although they mostly occur in children who are likely to grow out of the allergy.

If you are allergic to a food, the symptoms will usually appear within 30-60 minutes of having eaten it. Symptoms of the allergy that you or your child may develop include:

Urticaria: Hives and/or welts on the skin that can be itchy and sore. Sometimes, it feels as if the itch is underneath the skin. It can be distressing but is considered to be a mild allergic reaction.
Nausea, diarrhoea or a runny nose.
Swelling, particularly around the eyes and lips.
Anaphlyaxis: Swelling of the tongue and throat, which can potentially constrict breathing. This is a medical emergency and requires urgent attention.

The most important thing to remember about the symptoms of food allergy is that they will occur every time the suspected food is eaten, says clinical immunologist and allergist Dr Marianne Empson. “Every time the person eats the food they are allergic to they will react. If they don’t eat the food, they won’t react.”

If the symptoms occur irregularly after eating the suspected food, they are probably not related to food allergy, and should be investigated by your doctor.

Food allergy involves the immune system but food intolerance usually affects the digestive system. Reasons for food intolerance include lacking an enzyme to properly digest the food (such as lactose intolerance), sensitivity to preservatives, stress or digestive disorders such as irritable bowel syndrome or coeliac disease.

Dr Empson says it is important to always investigate suspected food intolerances with a medical professional to diagnose and treat the problem. The genetic condition of coeliac disease in particular can have serious health consequences and is on the rise — about one in 100 people have it.

Many people believe eliminating the suspected food from their or their child’s diet may be all that is necessary to treat themselves. However, it can be difficult to pinpoint the allergy-inducing food, and many people get it wrong, often compromising themselves nutritionally. The diagnosis of allergy should always be conducted by a medical professional who has experience with allergies.

Step 1

See your GP, who may recommend you for skin allergy testing, which will usually be done at a laboratory. Depending on the results, your GP can treat you or refer you to an allergy specialist.

Step 2

The gold standard, front-line approach for allergy testing is skin-prick testing, says Dr Empson. The results of this test must always be considered as part of a thorough medical history.

Skin-prick testing does just what it suggests — pricks the skin with a number of allergens to test for allergic reactions. Sometimes up to 20 foods are tested at once.

The allergens from the food — usually proteins — are contained in a tiny drop of commercially prepared liquid. The drops are separately and precisely placed on the skin and then pricked so a tiny amount of the drop enters the skin.

If you respond with a raised, red lump, it may indicate that you have antibodies that recognise the protein, which in turn release histamine, which produces the lump.

However, a positive response to a skin-prick test doesn’t necessarily mean you have a food allergy. Dr Empson says testing for food allergy can sometimes produce false positive results.

“If someone can eat the food, that is actually the best test. So if someone eats peanut all the time, and has skin tests that come up positive to peanut, if they’ve been able to eat then they’re not allergic to it.

If someone’s never eaten the food and get a positive response to it, then they shouldn’t try it.”

She adds that if someone thinks they have had an allergic reaction to a food and they’ve had a positive response, then it’s likely they are allergic to it.

However, trying a food you think you may be allergic to is not recommended outside of medical supervision, in case you have a dangerous reaction.

Other types of testing

Other types of testing for food allergies include RAST testing and serum-specific allergy IGE antibodies. These are essentially blood tests for antibodies specific to an allergen. They are, however, both much more expensive methods of testing for food allergy, and can be less accurate than skin testing.

“It’s just testing the blood, in much the same way as we test using the skin-prick test, looking for antibodies. But, instead of it being done as a skin-prick test on a patient it’s done in a laboratory,” says Dr Empson.

In fact, a negative blood test result will need to be followed up with skin testing as it is more sensitive.

The best treatment for food allergy is complete avoidance of the allergen, says Dr Empson.

“Education is phenomenally important and will help to prevent a lot of recurrences.”

Antihistamine is a good treatment for people who have had mild allergic reactions to food but adrenalin, in the form of an EpiPen that is prescribed by a doctor, is extremely important for people who have had anaphylactic reactions. Dr Empson also recommends some of her patients wear MedicAlert bracelets so they can get appropriate medical help quickly in the event of anaphylaxis.

Yes, allergies are on the increase. The frequency of allergic disease has approximately doubled in the past few decades. Why? We don’t know, but the following theories are being studied extensively:

  • We’re too clean: Our obsession with cleanliness eliminates exposure to bacteria that helps build our immune systems, and children are not being exposed to as many childhood illnesses.
  • Our diets have changed dramatically: We’re eating a lot of different foods than we used to, and potentially allergenic foods, such as dairy, eggs, peanut and soy are being introduced too late to babies, which may trigger an allergic response.
  • Pollution: Everyone has more exposure to chemicals in our day-to-day lives.

Adults with food allergy are far less common than children, but this is expected to rise as more children than ever are affected.

“Large numbers of allergic children haven’t reached adulthood, so we’re dealing with a different adult population to what we will be in 10 years,” says Dr Empson.

Seafood is the most common food adults are allergic to and the allergy is usually permanent once it happens. It can develop at any time, even to people who have always eaten seafood without a problem. No one knows why this happens, or how the immune system suddenly triggers into ‘attack’ mode for something it has previously not recognised as a foreign body.

Kids are the group most severely affected by food allergy. A recent Australian study found that one in 10 babies had allergies to eggs or peanut. But the good news is that most children will grow out of their allergy by around the age of five.

The most common foods children are allergic to are peanuts, eggs and milk. Peanut allergies tend to be more permanent — only around 20 per cent of children will outgrow them, although they are at risk of re-developing the allergy at some stage.

Studies are beginning to show that introducing allergenic food much earlier in a child’s life may reduce the incidence of food allergy.

One study looked at Jewish children living in the UK and Israel. The group in the UK, who did not eat peanuts, were 10 times more likely to have a peanut allergy than those in Israel, where the children ate large quantities of peanuts from very early in their life.

Dr Empson says doctors are now questioning whether previous advice of delaying the introduction of allergenic foods to children was the right thing to do.

Current advice is moving away from delaying the introduction of potential allergens, such as eggs, dairy, peanuts and soy, when introducing solid foods to infants. There’s no evidence that this helps avoid allergy, even for high-risk infants. However, introducing new foods one at a time over two to four days is advised so that any adverse reactions will be detected.


  1. Eliminate a food you think you may be allergic to without having a diagnosis, you could be wrong and do yourself more harm than good.
  2. Be fooled — the gold-standard, scientifically-proven test for diagnosing allergy is a skin-prick test that should only be done by a medical professional experienced with diagnosing and treating allergies.
  3. Believe kinesiology, electro-dermal testing, phototoxicity or IGG testing and Vega testing will work. There is no evidence to prove these methods are accurate and they can be very expensive.
  4. Panic — millions of people around the world enjoy happy and healthy lives living with allergy.
  5. Lose heart — there is a life after food allergy — you can still enjoy a healthy and delicious diet.


  1. Visit a dietitian (if you have a diagnosed food allergy), who can help plan your diet without missing out on vital nutrients.
  2. Talk to your doctor about re-testing if your child has an allergy or intolerance — it is possible to grow out of them.
  3. Do get organised with your diet once diagnosed — prepare your own food where possible, or check ahead with friends or cafés and restaurants to see if they can cater for your diet.
  4. Tell your family, friends, schools and workmates that you have an allergy, and let them know what help you need in the event of a severe reaction.
  5. Carry antihistamine in case of an allergic reaction and get a MedicAlert bracelet and an EpiPen if you have ever had an anaphylactic reaction.

Australasian Society of Clinical Immunology and Allergy www.allergy.org.au
Allergy Specialists www.allergy.org.nz


Date modified: 31 December 2020
First published: Oct 2012


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