INTRODUCING FOOD ALLERGIES

 

Australia and New Zealand have some of the highest rates of allergic diseases worldwide and food allergies are no exception. Food allergies affect up to one in ten children and rates are rising rapidly. Recent studies have discovered that allergy problems are more common in Westernised countries, and less common in developing countries.

In this part, we introduce the different allergic diseases (including food allergies), and look at the different rates of the allergic conditions around the world. We discuss some theories on why the allergic diseases are more common in some countries as compared to others, and explain how a person’s genes and the environment can both contribute to allergy problems. We then look at some things you can do to prevent your child from developing an allergic problem such as food allergy.

Food allergies are much more common now than they used to be. People often say to us ‘You know, when I was growing up, I didn’t know anybody who had a food allergy. Nowadays, it seems like everyone has one, or more!’ And it’s true. Just about everyone we meet knows someone with food allergies and almost every school or childcare centre has at least one enrolled child with food allergy.

In this chapter, we give you an overview of food allergies in Australia and New Zealand, including why rates of food allergy may be rising, and define some allergy jargon. We also cover prevention and management of food allergies, in the home and in settings such as schools and childcare centres, and teaching kids about food allergies. Finally, we look at what treatments are on the horizon.

Describing Food Allergies in Kids

The term food allergy is bandied about quite a lot, and is often used incorrectly to describe any bad reaction to a food. A lot of confusion also surrounds what a food allergy is and what a food intolerance is; many people use these labels interchangeably, but these are very different conditions. Because of this confusion, almost ten years ago the World Allergy Organization brought together a team of experts from around the globe to develop consensus definitions describing the different reactions to foods.

These experts decided that any reaction to a food that’s reproducible would be called a food hypersensitivity, and that these food hypersensitivities could be divided into either food allergies or food intolerances depending on what was causing the reaction.

Reacting badly to food

The body can react badly to a food for many different reasons. For example, a reaction may occur because of chemicals in the food itself, because the body can’t break down the food properly or because the person’s immune system has recognised the food as harmful and so reacts to the food.

Your immune system is an enormously complex army of cells that has the express purpose of protecting you from foreign invaders. The immune system has many parts to its army, each with a specific job of defending your body against a specific invader. This helps to protect you from infections. However, sometimes the immune system gets it wrong and recognises something as harmful even when it’s not. (This same type of error is responsible for causing autoimmune conditions such as diabetes and multiple sclerosis. In these conditions, the immune system’s mistake is to recognise parts of the body as being harmful when they’re not.)

When the immune system incorrectly interprets food as harmful, you get a food allergy. Now, each time people with egg or peanut allergy eat egg or peanut, their immune system reacts to the food and causes an allergic reaction.

Defining the difference between food allergies and intolerances

Most people have experienced an episode where a certain food didn’t agree with them. Indeed, more than 25 per cent of people are believed to have experienced an adverse reaction to a food on a regular occasion at least some time in their life.

Not all reactions to food are caused by an allergic mechanism. Adverse reactions to food can result from intolerances (such as lactose intolerance), food poisoning (from foods contaminated with bacteria or toxins), or from other illnesses, such as irritable bowel syndrome, reflux, inflammatory bowel disease or migraines.

The term food intolerance is used to describe all reproducible reactions to foods that aren’t food allergies. While food allergies are caused by the immune system recognising the food as harmful (see the preceding section), food intolerances are caused by substances within the food itself that can cause a bad reaction (such as scromboid food poisoning, from eating bad fish, or histamine-releasing compounds in tomatoes and strawberries), or problems in the body that make it difficult to digest the food (such as lactose intolerance, when a person lacks the enzyme lactase that breaks down lactose in foods.

Distinguishing between food allergies and other forms of adverse reactions to food is important, because food allergies, and more particularly IgE mediated food allergies, are the only types of reaction that are associated with anaphylaxis (a severe allergic reaction affecting the breathing or circulation) — which can be life-threatening. 

If your child has food allergies and is at risk of anaphylaxis, you need to take very stringent measures to avoid the food that causes the allergies. People with food intolerances may experience unpleasant symptoms if they accidentally ingest a certain food, but they aren’t endangering their lives. Chapter 7 looks at how you can manage your child’s food allergy.

Pointing the finger at common allergies in kids

The most common allergies in children are to egg, milk and peanut, followed by soy, wheat and tree nuts. Children can also develop allergies to fish and shellfish, although these more commonly develop in adults. These eight food groups cause more than 90 per cent of all food allergies (see Chapter 4 for more details on foods that cause allergy). Doctors don’t fully understand why these particular foods are more likely to cause allergy while all the other foods in the diet don’t; many researchers are investigating this.

Even though most food allergies are caused by just a small number of foods, a person can develop an allergy to any food provided the food contains protein or complex carbohydrate molecules that can be recognised by the immune system — the immune system can’t bind to or recognise small molecules such as sugar or salt, so being allergic to these types of simple molecules isn’t possible, even though some parents have come to see us because they thought their child was allergic to sugar!

Food allergies can be caused by unusual foods that are only eaten in some regions of the world. For example, in South-East Asian countries such as Singapore, bird’s nest soup (made from the saliva nests of certain birds) is a delicacy and children can develop allergy to bird’s nest.

Busting myths about anaphylaxis

Anaphylaxis is a severe allergic reaction that’s life-threatening. This reaction is the most severe form of an immediate, or IgE mediated, food allergy reaction, and can only occur in children with IgE mediated food allergy.

Children with delayed food allergies such as the non-IgE mediated food allergies or the mixed IgE and non-IgE mediated food allergies don’t develop anaphylaxis.

The term anaphylaxis is used when an IgE mediated food allergy reaction affects the airways (breathing) or the circulation. If the breathing system is affected, you can have difficulty breathing, a hoarse voice, persistent coughing, or noisy breathing (wheezing or stridor). If the circulation is affected, children (especially babies) become pale and floppy or they may even collapse (although this is rare). The situation is very serious if the circulation becomes involved, because this is considered to be the most severe type of anaphylaxis.

While food allergies are common in children, affecting up to 10 per cent of children in Western countries, most food allergy reactions aren’t life-threatening and are mild to moderate in severity, causing hives, swelling, vomiting, tummy pain or diarrhoea. Severe reactions (anaphylaxis) are less common, and only about 1 per cent of children with food allergy will have anaphylaxis.

The important thing is to know how to recognise a severe reaction so that you can act quickly and confidently to initiate the correct care as quickly as possible.

Anaphylaxis to foods is most common in young children under the age of five years and less common in adolescents and adults. But anaphylaxis reactions in adolescents and young adults aged 10 to 35 years are more likely to result in death.

Mimi’s own research found that in the nine years between 1997 and 2005, only seven deaths due to food anaphylaxis occurred in Australia, with six of these seven deaths occurring in children and young adults aged between 10 years and 35 years, and no deaths in children under five years of age. This means the end of primary school and the secondary affected, children (especially babies) become pale and floppy or they may even collapse (although this is rare). The situation is very serious if the circulation becomes involved, because this is considered to be the most severe type of anaphylaxis.

While food allergies are common in children, affecting up to 10 per cent of children in Western countries, most food allergy reactions aren’t life-threatening and are mild to moderate in severity, causing hives, swelling, vomiting, tummy pain or diarrhoea. Severe reactions (anaphylaxis) are less common, and only about 1 per cent of children with food allergy will have anaphylaxis.

The important thing is to know how to recognise a severe reaction so that you can act quickly and confidently to initiate the correct care as quickly as possible.

Anaphylaxis to foods is most common in young children under the age of five years and less common in adolescents and adults. But anaphylaxis reactions in adolescents and young adults aged 10 to 35 years are more likely to result in death. school years are the times of increased risk for children with food allergies.

Help your child learn how to manage food allergies as she comes to the end of primary school so that she can take greater responsibility for managing her condition while not with you. Learning about food allergies, how to avoid food allergens, and how to manage allergic reactions should be part of your child’s preparation for starting secondary school. 

No reliable method of predicting who’s likely to have anaphylaxis and who’s not is yet available. No skin test or blood test can identify with certainty at-risk children. Fortunately, however, some clinical signs can help doctors identify children who might be at greater risk of anaphylaxis. Your child’s doctor takes these and other factors into account when developing a management plan for your child. 

Understanding Why Some Kids Have Allergies and Others Don’t

Parents we talk to are often dismayed that one of their children has a allergy does tend to run in families, researchers can’t find any direct inheritance links. In fact, food allergies appear to have lower family history risks than other allergic diseases such as eczema, asthma and hay fever. Why this may be is anyone’s guess, but what we can take from this evidence is that genes play some part in the risk of developing food allergy but they’re by no means the major driver of disease risk. Lifestyle factors are far more likely to cause food allergies than inheriting allergy genes from your parents.

Getting a Grip on Allergy Jargon

Here we clarify some of the different terms we use throughout the book. What do we mean when we say, ‘Sophie has food allergy’, ‘Thomas has anaphylaxis’, ‘Jessica has asthma’ or ‘Your husband is allergic to the vacuum cleaner’? And what does it mean if someone is atopic or lactose intolerant?

Understanding allergies and allergic reactions

An allergy occurs when your immune system recognises a substance in your environment as harmful and so mounts an immune response to that substance, which can then lead to symptoms of an allergic reaction every time you’re re-exposed to that substance.

Food allergy is a very good example of an allergy. If you have an IgE mediated allergy to peanut, your immune system has recognised various proteins in the peanut (peanut allergens) as harmful and generated allergy antibodies (IgE antibodies) against these peanut proteins. Now, each time you eat peanut, you develop an allergic reaction with symptoms such as hives, swelling of the face, vomiting or even anaphylaxis.

IgE antibodies are one type of antibody that the immune cells called lymphocytes can make. These antibodies are really designed to protect you from worm and parasite infections; however, when you develop an allergy, the immune system has instructed the lymphocytes to make IgE antibodies that recognise food or environmental allergens that you’re allergic to, even though these allergens are harmless. These IgE antibodies circulate in the blood and also bind tightly to specialised allergy cells, called mast cells, which sit in the skin, airways and intestines. If the IgE antibodies on the surface of mast cells encounter the allergen that they recognise, they bind to the allergen (much like a lock and key) and this binding process activates the mast cell to release a range of allergy factors that cause the allergic reaction. 

The immune mechanisms that cause the non-IgE mediated and mixed IgE/non-IgE mediated food allergies (also known as delayed food allergies — see the section ‘Knowing the Symptoms’, later in this chapter, for more) are less well understood, but don’t appear to involve the IgE antibody or binding of the IgE antibody with the allergen. Instead, other immune cells, such as eosinophils and lymphocytes, are likely to be responsible for these delayed types of food allergies.

People can have allergies to foods, drugs, insect venoms and even latex, and allergies to all of these substances are examples of an allergic disease.

Comprehending allergic diseases

Allergic diseases are a group of conditions that are all caused by unwanted immune responses that lead to inflammation in tissues, where that inflammation involves the presence of allergy cells and allergy promoting factors such as mast cells, IgE antibodies, T helper type 2 lymphocytes, or eosinophils.

The allergic diseases are;

1.  Asthma

 2. Eczema (also known as atopic dermatitis)

 3. Hay fever (also known as allergic rhinitis)

4.  Food allergy

 5. Drug allergy

 6. Insect sting allergy

 7. Other specific allergies (for example, to latex or blood products)

So, food allergy is just one of the allergic diseases. And asthma and eczema are also allergic diseases but aren’t allergies.

For the specific allergies, such as food allergy or bee sting allergy, the allergic inflammation only occurs when you’re exposed to the thing (allergen) that you’re allergic to. So, you can be symptom-free if you avoid the allergen that triggers your symptoms. This is an important difference between the specific allergies and the other allergic conditions.

Asthma, eczema and hay fever aren’t caused by an allergy. In asthma, eczema and hay fever, the immune system generates an unwanted inflammatory response in a target tissue (airways, skin or nasal passages) for an unknown reason. Many people mistakenly believe that asthma, eczema and hay fever are caused by an allergy to something, and that if this ‘something’ can be avoided, the asthma, eczema or hay fever will go away and they will be cured. This isn’t the case. However, people with asthma, eczema or hay fever often also have an allergy to something, and exposure to the allergen can make their asthma, eczema or hay fever symptoms worse by triggering and/or aggravating the allergic inflammation. For example, most people with asthma, eczema or hay fever have an allergy to house dust mite, and exposure to dust mite can worsen their condition. The dust mite allergy isn’t the cause of their disease but it can make things worse.

So, food allergy is just one of the allergic diseases. And asthma and eczema are also allergic diseases but aren’t allergies.

For the specific allergies, such as food allergy or bee sting allergy, the allergic inflammation only occurs when you’re exposed to the thing (allergen) that you’re allergic to. So, you can be symptom-free if you avoid the allergen that triggers your symptoms. This is an important difference between the specific allergies and the other allergic conditions.

Asthma, eczema and hay fever aren’t caused by an allergy. In asthma, eczema and hay fever, the immune system generates an unwanted inflammatory response in a target tissue (airways, skin or nasal passages) for an unknown reason. Many people mistakenly believe that asthma, eczema and hay fever are caused by an allergy to something, and that if this ‘something’ can be avoided, the asthma, eczema or hay fever will go away and they will be cured. This isn’t the case. However, people with asthma, eczema or hay fever often also have an allergy to something, and exposure to the allergen can make their asthma, eczema or hay fever symptoms worse by triggering and/or aggravating the allergic inflammation. For example, most people with asthma, eczema or hay fever have an allergy to house dust mite, and exposure to dust mite can worsen their condition. The dust mite allergy isn’t the cause of their disease but it can make things worse.

All about asthma

Asthma is an allergic disease involving allergic inflammation of the airways. This condition is the most common of the allergic diseases, and affects one in five Australian children, one in seven teenagers and one in ten adults. The condition is more common in boys during childhood, but more common in women after the teenage years.

In asthma, the chronic inflammation in the airways results in the airways being over-reactive — the airways contract more often and to a greater degree when exposed to things (such as cold air, exercise or cigarette smoke) that may not bother people who don’t have asthma. Most children with asthma also have allergies to airborne allergens (such as pollen, dust mite and pet danders) and exposure to these allergens can trigger inflammation in the airway and cause asthma symptoms.

People with asthma are more likely to have other allergic diseases such as hay fever, eczema and food allergy. Foods rarely cause asthma symptoms (fewer than 2 per cent of people with asthma get symptoms of asthma due to a food), but having both asthma and food allergy makes you more likely to have a severe reaction to the food you’re allergic to and also more likely to have a severe asthma attack.

Asthma is also an important risk factor for death due to a food allergy reaction so if your child has a food allergy and also has asthma, making sure that the asthma is well controlled is really important. 

Take your child to see your doctor if your child has an asthma attack more than once every few months or if your child’s asthma symptoms are noticeable every week.

Everything eczema

Eczema is an allergic disease where allergic inflammation occurs in the skin. The condition most commonly develops in the first six months of life and affects about one in five infants. It usually improves after the first three to five years of life; however, while some children outgrow their eczema, many continue to have eczema as adults.

The allergic inflammation in the skin causes a rash that is red, scaly and itchy. If your child scratches at the rash, it is worsened and, if untreated, can cause the skin to thicken. Most children with eczema, like those with asthma, also have allergies to airborne allergens (particularly house dust mite) and exposure to these allergens can trigger or worsen eczema symptoms. Some children, especially young babies with severe eczema, can also have food allergies and exposure to those foods can trigger or worsen eczema symptoms.

As well as scratching the skin and specific allergies, many other factors can make the inflammation in the skin that occurs with eczema worse, such as stress, overheating, bacteria on the skin, having vaccinations and teething.

Eczema and bacteria

Everybody carries bacteria on the skin, and the most common skin bacterium is called staphylococcus. Children with eczema carry more staphylococci on their skin than children who don’t have eczema, and staphylococcus is a very potent trigger of inflammation in children with eczema — much more potent than any airborne or food allergens. Reducing bacterial loads on your child’s skin by bathing daily with non-soap cleansers is one of the most effective ways to improve their eczema. Infection of the eczema with staphylococcus is also very common and, if this happens, your child needs antibiotic treatment in order for the rash to heal.

Like asthma, many children with eczema have other allergic diseases, particularly asthma and food allergy. Recent research suggests that having eczema may increase your chances of developing the other allergic diseases — being exposed to allergens through broken skin is more likely to result in a person being sensitised to that allergen, rather than developing tolerance to that allergen, whereas being exposed to an allergen by eating the allergen is more likely to result in a person developing tolerance to that allergen. If this turns out to be correct, improving the skin barrier in children with eczema may offer one approach to preventing food allergy in these children.

Having a look at hay fever (allergic rhinitis)

Allergic rhinitis, also known as hay fever, is an allergic disease involving inflammation in the inner lining of the nose. This allergic inflammation causes symptoms of sneezing, itchy and runny nose, and blockage of the nose (congestion). Often symptoms affecting the eyes (allergic conjunctivitis) also occur, with itchy, red, watery eyes. Children usually develop allergic rhinitis a little later than eczema and asthma — usually at around three to five years of age.

Children with allergic rhinitis are often allergic to house dust mite, pollens and pet danders and inhaling these allergens can trigger inflammation in the nose. In addition, as with asthma and eczema, when inflammation in the lining of the nose is already apparent, many other factors can also trigger symptoms including irritants such as strong smells, cigarette smoke and dry air.

Many people believe that allergic rhinitis is a trivial condition and tend to ignore symptoms in themselves and their children. However, allergic rhinitis has the same impact on quality of life as asthma does, and has been shown to reduce concentration and learning at school, affect sleep and cause other health problems such as ear infections and sinus infections. If you have both allergic rhinitis and asthma, poorly managed allergic rhinitis can make your asthma worse, increasing the chances and severity of an asthma attack and admission to hospital for asthma. So controlling and managing allergic rhinitis is just as important as for asthma and eczema, and this involves controlling the inflammation with topical corticosteroids.

Defining atopy

Most people with allergic disease(s) have an underlying genetic tendency or predisposition to develop unwanted allergic responses to allergens, which is called atopy.

If you have this genetic predisposition, or atopy, you’re more likely to develop an allergic disease and make allergy antibodies (IgE antibodies) to substances in the environment that are normally harmless (such as foods or pollen). When you make allergy antibodies to an allergen, you’re said to be sensitised to that allergen. But not all people who are atopic develop an allergic disease — just as not all people who are sensitised develop an allergic disease.

Taking on the atopic march

If you’re a parent, you’ve probably heard the terms atopic march or allergic march and wondered what they mean. No, they’re not a marching band! These terms have been used to describe the progression of allergic disorders during childhood.

Food allergy and eczema are typically the first allergic conditions to develop and usually present in the first 3 to 12 months of life. The most common food allergies at this age are egg, milk and peanut allergy, and these peak at around one to two years. Most food allergies (including egg, milk, wheat and soy) resolve in later childhood so that the overall prevalence of food allergy reduces after five years of age and stabilises from adolescence onwards. Peanut and tree nut allergies tend to persist into adulthood, and allergy to shellfish and fish commonly present for the first time in young adults, so that the most common food allergies in adults are peanut, tree nut, shellfish and fish allergy.

Asthma and allergic rhinitis generally have a later onset, at around three to five years of age. Some children have wheezing illness in the first year of life, but most asthma starts around preschool age, and asthma prevalence increases steadily into the school years before plateauing. Allergic rhinitis continues to increase in prevalence through to adult life. This pattern of eczema and food allergy appearing in the early months of life, followed by later development of asthma and then allergic rhinitis is what’s described as the allergic or atopic march.

Having one allergic disease increases the chances that you develop other allergic diseases, and many children who have eczema or food allergy go on to develop asthma and hay fever. This doesn’t mean that one allergic disease is the cause of other allergic diseases. More likely, people develop more than one allergic disease because they have an underlying atopic predisposition, and so are at greater risk of developing any of the allergic problems.

Watching Allergy Rates Rise

A rapid rise in all of the allergic conditions (asthma, eczema, hay fever, food allergy) has occurred in the last 30 to 50 years, mainly in countries with a Westernised lifestyle. Rates of asthma were the first to rise, increasing rapidly from 1980 onwards. More recently, asthma rates have stabilised or even fallen in some countries, while rates of eczema and allergic rhinitis are still increasing but at a slower rate. In contrast, food allergies and anaphylaxis started to increase somewhat later, in the 1990s, and are rising at an exponential rate.

Researchers know that both people’s genes and their environment contribute to the regulation of their immune system and so can determine whether a person develops one of the allergic diseases. However, the rapid rise in allergy problems in the last half of a century tells experts that this increase must relate to changes in the environment rather than to changes in people’s genes, because this time frame is too quick for genes to have shifted to any great degree. Because these increases have mainly affected developed countries, experts also believe the environmental factors driving the rise in allergic diseases are likely to relate to the Western lifestyle.

Several factors are thought to be especially important:

 Improved living conditions with increased sanitation and reduced infections. The association between improved living conditions and allergies is known as the hygiene hypothesis or microbial hypothesis. Researchers now believe that the overall reduction in exposure to microbes has influenced allergic disease rates, rather than just the lower rates of infection in Westernised countries. Diverse and abundant microbial exposures in early life play an important role in the development of a healthy immune system that averts allergic responses.

 Reduced UV exposure and vitamin D.

 Delayed introduction of allergenic foods.

 Reduced exposure to other immunomodulatory diet factors, such as omega 3 fatty acids (fish oils).

Foiling Food Allergies: Prevention versus Cure

Unfortunately, at the moment, doctors can recommend very few things for the prevention of allergic diseases, including food allergy. This is partly because researchers are still trying to understand the factors that contribute to the development of allergic disease. If the important factors driving allergy problems can be identified, developing effective ways to prevent or reduce the risk of a child developing allergic diseases, including food allergy, may be possible.

The guidelines for prevention of allergic disease only apply to children at increased risk for developing allergy problems — that is, children who have a first-degree relative (mother, father or sibling) with one of the allergic diseases. However, because of the high rates of food allergy in Australia and New Zealand, more than 50 per cent of babies are at increased risk of allergic disease and so these guidelines apply to the majority of babies rather than the minority:

 Breastfeed for at least six months, or if the mother is unable to breastfeed during this time, introduce a hypoallergenic hydrolysed HA baby formula (such as Nan HA or Karicare Aptamil).

 Introduce complementary solid foods, from around four to six months — don’t avoid the allergenic foods. This applies to all babies, not just those at increased risk of having an allergic disease.

 Avoid exposure to cigarette smoke during pregnancy and early childhood.

Note: The guidelines outlined in the preceding list are based upon ASCIA guidelines that are similar to those in the United Kingdom, European Union and United States. The Cochrane meta-analysis evaluating the effects of HA partially hydrolysed formulas on the prevention of allergic disease are being updated to include recent studies that have reported conflicting results. As expert guidelines are based upon the findings from Cochrane and other meta-analyses.

No evidence exists that elimination diets in the mother during pregnancy or breastfeeding prevent allergic disease in the baby, and these aren’t recommended.

Knowing the Symptoms

Food allergy reactions can be mild, moderate or severe. The symptoms of an IgE mediated food allergy reaction are much the same for allergies to all types of foods. Allergists usually divide food allergies into two categories:

 IgE mediated food allergies (also known as immediate food allergies). Symptoms include hives (itchy lumps that look like mosquito bites), swelling of the face, eyes or mouth, vomiting or anaphylaxis (when the breathing or circulation is affected). All of these symptoms usually occur within minutes of food ingestion, although some symptoms, such as vomiting, diarrhoea or an eczema flare, may occur up to a few hours later. 

 Non-IgE mediated and mixed IgE/non-IgE mediated food allergies (also known as delayed food allergies). Symptoms associated with delayed reactions are usually gut problems, with the most common symptoms being vomiting, diarrhoea, abdominal pain and colic, usually occurring several hours after ingestion of the food. 

An important difference between delayed (non-IgE mediated and mixed IgE/non-IgE mediated) and the immediate (IgE mediated) food allergies is that delayed food allergies don’t cause anaphylaxis, or hives or swelling of the face, which are characteristic of the IgE mediated immune reactions.

Testing Times: Finding the Cause of Allergic Reactions

An allergy test that looks for allergen-specific IgE antibodies (allergy antibodies that recognise allergens) shows if your child has made an IgE antibody against a particular food. Allergen-specific IgE antibodies can be measured in the skin (skin prick test) or in the blood. The presence of this allergen-specific IgE antibody against a food only means that your child has become sensitised to that food — or, in other words, that your child’s immune system has recognised that food and mounted an immune response to it. The presence of these antibodies doesn’t always mean that your child is allergic to the food. (Indeed, in more than 50 per cent of positive allergy tests, the child doesn’t have a clinical allergy to that food and can tolerate that food just fine without having any bad reaction.)

The reasons only some children who have made allergy antibodies to a food are allergic to the food aren’t understood, and this is an important area of research that we are both involved with. In our research, we’re trying to discover what protects some children from having a clinical allergy even when their immune systems have already recognised the food and made allergy antibodies to the food.

Nevertheless, if a child has experienced a reaction to a food that fits with an IgE mediated food allergy and the subsequent blood or skin allergy test is positive for that food, this confirms that the child has IgE mediated food allergy to that food. So these allergy tests are very helpful to doctors when diagnosing food allergies in children.

Researchers have shown that the higher the level of the specific IgE antibody to a food, and the larger the skin prick test size, the more likely it is that the child does in fact have a clinical allergy. Based on this information, researchers have developed 95 per cent thresholds for skin prick tests and the allergen-specific IgE blood tests to the common food allergens. These thresholds allow the tests to predict, with 95 per cent certainty, that the child has clinical food allergy rather than just being sensitised to the food, even if the child hasn’t experienced a reaction to that food.

Checking for immediate food allergies

The most common food allergy tests for immediate or IgE mediated food allergies (listed in order of most common) are

 Skin prick tests: Allergen-specific IgE can be detected in the skin using a skin prick test (SPT), which introduces a small amount of allergen into the skin. When the allergen binds to allergen-specific IgE antibodies on the surface of mast cells, the mast cells are activated and release a host of immune factors that cause redness and a wheal (bump on the skin) at the site of the skin test. The result is obtained by measuring the size of the wheal. The higher the level of allergen-specific IgE in the body, the bigger the wheal caused by the SPT. A positive test is defined as a wheal that’s at least 3 millimetres larger than the negative control (saline is used as a negative control and should not cause a wheal on the skin).

 Note: The SPT wheal reaction can vary depending on who does the test, which skin test device is used, the time of day and where on the body the test is done; these factors must be taken into account when interpreting the skin test result.

 Blood tests: The level of allergen-specific IgE in the blood can also be measured. These tests are very accurate and reproducible and aren’t affected by the time of day or other factors that can affect the SPT. However, the test is more expensive and takes longer to provide a result, so the SPT is usually preferred by most allergists.

 Food challenges: Challenges are the gold standard tests for diagnosing all food allergies — both the IgE mediated and the delayed food allergies. The food challenge test involves giving a child the food in question, starting with small amounts and progressively increasing the amount every 15 to 20 minutes, while watching to see if a reaction develops. The food challenge test is positive if a reaction develops and negative if the child completes the challenge and takes a standard serving of the food without reacting.

Testing for delayed food allergies

In contrast to the IgE mediated food allergies, no blood or skin tests can diagnose non-IgE mediated and mixed IgE/non-IgE mediated food allergies, also known as the delayed food allergies. For these food allergies, doctors make a diagnosis based upon the history and examination findings, together with seeing what happens when the food in question is taken out of the diet and then put back (a food elimination and reintroduction challenge).

If symptoms improve with elimination of the food and recur when the food is reintroduced, this confirms the diagnosis of a non-IgE mediated food allergy or a mixed IgE/non-IgE mediated food allergy. If the doctor is certain that the food allergy doesn’t involve an IgE mediated component (that is, the allergen-specific IgE blood test or the skin prick test are negative), reintroducing the food at home is safe.

In some cases, an endoscopy test may be used to help with diagnosing non-IgE and mixed IgE/non-IgE mediated food allergies. This test is performed by gastroenterologists (physicians specialising in gut conditions), allowing the specialist to look inside the gut and to take samples of the intestine wall for more detailed examination under the microscope. Non-IgE mediated and mixed IgE/non-IgE mediated food allergies can cause inflammation in the intestinal wall, so looking for these signs can help to confirm the diagnosis.

Managing Allergies Day by Day

Looking after a child with food allergies can be a daunting task for parents, and for any school and childcare staff, family and friends also responsible for the child. How do I manage my child’s allergies? What if Jack has an allergic reaction when he comes over to play with Harry? 

What will I do if Susie has anaphylaxis? How do I treat an allergic reaction? Should I let Ellie eat Sarah’s birthday cake? All of these questions can flood into your head when you discover you have or you’re going to be looking after a child with food allergy.

Four key elements are involved in managing food allergies:

1. Avoid food allergens. Read ingredient labels looking for the allergen that your child is allergic to. 

2. Manage situations that have an increased risk for your child accidentally eating their food allergen. Develop specific strategies for these high-risk situations, which include going to a friend’s home, eating out at a restaurant, or going to a party, the movies or other event. If your child is old enough, teach your child about taking extra care to ensure any food she eats doesn’t contain the food allergen that she’s allergic to.

 3. Learn how to recognise an allergic reaction and how to treat an allergic reaction in an emergency. You and other people caring for your child, as well as your child if he’s old enough, must learn about how to recognise an allergic reaction and the emergency management of allergic reactions. All of this information is contained in the medical emergency action plan that your child’s doctor should prepare for your child, and update each year.

4. Control medical problems such as asthma or heart conditions, which can increase the risks of anaphylaxis. Many children with food allergies also have asthma, and asthma is known to be a risk factor for having a severe food allergy reaction (anaphylaxis), as well as for an anaphylaxis reaction causing death. Children with food allergies who have asthma should be reviewed regularly to ensure that their asthma is well controlled. Other medical problems that can increase the risk of anaphylaxis reactions, such as heart conditions, should similarly be reviewed regularly to ensure they’re properly managed.

As part of the ongoing management of your child’s food allergy, your child should be reviewed by a doctor (either your child’s GP or paediatrician, or an allergist) every year. At this annual visit, the doctor can review your child’s diet and ability to avoid the food allergen, confirm that your child’s diet is nutritionally adequate (this may require referral to a dietitian), and remind you and your child about high-risk situations for accidental exposure to food allergens. The doctor can also update your child’s emergency action plan, re-educate you on all aspects of this plan, and review whether your child needs an adrenaline auto-injector if not already prescribed with one.

Importantly, the doctor can review your child’s asthma and any other medical conditions that can increase the risk of anaphylaxis to ensure that these are properly managed and well controlled.

Written by Glenn Lumsden in "Kid's Food Allergies For Dummies", Australian New Zealand Edition, Assoc. Prof. Mimi Tang & Assoc. Prof. Katie Allen (Melbourne/Murdoch), Wiley Publishing Australia, 2012, excerps chapter one. Digitized, adapted and illustrated to be posted by Leopoldo Costa.