Kids & Food: How to tell the difference between allergies and intolerances

Talk of allergies has never been more prevalent. Everyone seems to have one… But do they? Dr. Clare Thompson discusses the difference between having an allergy and being intolerant.


Allergies must be catching because everyone I know seems to have one. Some parents claim their child is allergic to everything and can’t eat wheat, dairy, gluten or sugar in general. However, the term ‘allergy’ is a complete misnomer and what parents often mean is that their child is intolerant rather than allergic.

Some of the symptoms of food intolerance and food allergies are similar, but the differences between the two are very important. Eating a food you are intolerant and sensitive to can leave you feeling miserable. However, eating a food you have a true allergy to can cause rapid and life-threatening symptoms to occur.

The Food Allergy Research and Education Department (FARE) report that the economic cost of children’s food allergies and intolerances is nearly $25 billion per annum in the USA. According to a study by the Center for Disease and Control Prevention (CDC) food allergies among children increased 50% from 1997 – 2015 but there is no clear answer as to why this is happening. In Europe, more than 17 million people are allergic or intolerant to a food group and hospital admissions for allergies in children are on the rise.

Every three minutes, a food allergy reaction sends someone to the emergency department which equates to more than 200,000 visits to the ER per year. A reaction from food can vary from a localised skin complaint (itchy mouth) to life-threatening anaphylaxis. Data shows that teenagers and young adults seem to be the group who are at the highest risk of fatal food-induced anaphylaxis.

Children with food allergies are four times more likely to have other atopic conditions (asthma and eczema) than those who do not. Interestingly many children do grow out of their food sensitivities, especially those to milk and eggs. Although there is no cure for true food allergies, it is worth seeking an opinion every few years with an allergy specialist to see whether your child might be growing out of theirs.

Food Allergies

Allergies are a function of our immune system which is the body’s natural defence system. When the body encounters an allergen (foreign material e.g food) this can cause the production and release of an immunoglobulin (protein) called IgE which is released to ‘protect’ the body against the foreign substance. An immune reaction is then triggered in the body which results in rapid and severe symptoms that can affect both the gastrointestinal system and airways of the child. Common symptoms of a true food allergy include:

  • itching and swelling of the skin (urticaria)
  • swelling of the tongue and closing of the airways (angioedema)
  • flushing of the face and wheezing
  • sudden onset of diarrhoea and vomiting
  • sudden drop in blood pressure


This describes the most severe form of an allergic reaction to a food where there will be sudden onset of difficulty in breathing, dizziness, tongue swelling, airway closure and sometimes loss of consciousness. Without immediate treatment with an injection of adrenaline (Epipen) anaphylaxis can be fatal.

Thankfully true food allergies are relatively rare affecting approximately 2% of the adult population. Common allergens include:

  • Peanuts
  • Tree nuts (walnuts, almonds, brazil nuts)
  • Eggs
  • Milk
  • Fish or shellfish
  • Sesame
  • Soya
  • Wheat

How to test for food allergies

Children who are truly allergic to a food group will require formal skin-prick testing in an allergy clinic with IgE levels (also called RAST testing) before they are administered with an Epipen and their caregivers will be trained on how to use it properly. Sometimes, physician-supervised oral food challenges (the gold standard) will also be performed under medical supervision to confirm the diagnosis.

Food Intolerances

A food intolerance takes place in the digestive system alone and is much more common than a true food allergy in the population. It occurs when you are unable to properly breakdown the food. This could be due to enzyme deficiencies (breakdown proteins), sensitivities to food additives or reactions to naturally occurring chemicals in foods. Often, people can even eat small amounts of the food without any problems at all but larger quantities may bring on symptoms.

Although not life threatening it can make the sufferer extremely uncomfortable from a few hours to several days. The symptoms are variable between different people and often quite vague and non-specific. Food intolerance do not involve IgE antibodies or the immune system and the mechanisms for most food intolerances are not entirely clear. Reactions are usually delayed, occurring several hours and sometimes up to days after exposure to the offending food group.

The symptoms caused by food intolerances usually affect the gut primarily but can include:

  • Diarrhoea
  • Bloating
  • Constipation
  • Eczema
  • Joint pain
  • Headaches
  • Lethargy

Examples of food intolerances include lactose in which people do not have the enzyme (breakdown protein) called ‘lactase’ to process it. Other people might react to chemicals that are produced naturally in caffeine or salicylates and histamines produced naturally from strawberries and ripe cheeses. Another cause of food intolerances include the addition of sulphites which are added to processed foods to extend their shelf life. These are also found in fruit juices and wine products.

Food intolerance is also postulated to be caused by different factors such as lifestyle and erratic food intake or high intake of refined foods with low nutritional content. Because it is possible to be intolerant to several different food groups at once it can be difficult to identify specific offenders. Sometimes these patients may have underlying bowel or skin conditions associated which can cloud the diagnosis further.

How to test for food intolerance

The only reliable way to test for food intolerance is by keeping a very clear diary of food and symptoms for a period of at least two weeks alongside a food exclusion diet.

Your child should be referred to a registered dietician who will take an extensive food history and carefully formulate an exclusion diet with one food group at a time to isolate the offending source. The exclusion diet needs to be strictly adhered to for at least two weeks followed by a food challenge in a controlled setting to observe cause and effect over the next 24 hours.

You should always seek the advice of a dietician before excluding food groups from your child’s diet in this manner as they may be unnecessarily missing out on key nutrients needed to meet their nutritional requirements for growth and good health.

Celiac Disease

Celiac disease is not an allergy or an intolerance, rather it is a lifelong auto-immune condition where the immune system recognises substances found inside gluten as a threat to the body and attacks them. Gluten is a protein found in wheat, barley and rye. 1 in 100 people are affected and it often follows a pattern of genetic inheritance.

When a celiac sufferer eats gluten their immune system reacts rapidly to cause the gut to become inflamed in the small intestine. The symptoms include bloating, diarrhoea, nausea, constipation, weight loss and rashes. Dermatitis herpetiformis is an itchy rash which is specific to Celiac disease.

Most people are diagnosed in childhood or early adulthood and the diagnosis is usually confirmed by a blood test and on a biopsy of the small intestine. The treatment is lifelong abstention from gluten products.

Food Poisoning

A reaction to a food that has ‘gone off’ will cause food poisoning (E.g. Salmonella) and will affect everyone who has consumed the product with sudden onset of vomiting for 2-3 days and diarrhoea for 5-7 days. This is very different to allergies and intolerances.

Can my child outgrow their food allergy?

I find it quite interesting that there are ever more parents presenting to see me with babies and children who seem to be intolerant and allergic to various food groups. One hypothesis is the way that food is processed and preserved to extend the shelf-life for wholesale in the 21st century. Clearly our bodies are not able to breakdown pesticides and sulphites in preservatives which are used on most produce we buy in our local supermarkets. Short of eating everything home-grown and organic it is incredibly difficult to be so puritanical from day-to –day and is not the most cost effective way of preparing meals for the family.

A study published in the Allergy, Asthma and Clinical Immunology Journal in July 2013 reported that a little more than a quarter of children outgrow their allergies at an average age of 5.4 years old. Children who were allergic to milk, egg or soy were the most likely to outgrow their allergies whereas the likelihood of outgrowing an allergy to shellfish, tree nuts and peanuts was significantly lower. Additionally, the earlier a child’s first reaction, the more likely that child was to outgrow the allergy.

Other factors that contributed to outgrowing an allergy or intolerance included having a history of only a mild reaction and being sensitive to only one food group. Studies have also shown that African-American children are less likely to outgrow their allergy than Caucasian children and boys are more likely to outgrow their allergy than girls.

Peanut allergy tends to be lifelong and only about 20 percent of children are fortunate enough to grow out of it. A Canadian research team in Montreal found that children are most likely to outgrow their peanut allergy by age 6 if it were to occur. After age 10 the chance of spontaneous resolution is much lower. One wonders whether this is all due to the immune system maturing as the child grows and much research is still being done globally to study and understand the nature and progression of food allergies.

Summary and key take-home messages:


Food Allergies


  • The immune system over reacts to a food that is typically harmless
  • Reactions usually comes on suddenly
  • A small amount of food can trigger the reaction
  • The reaction is reproducible every time you consume that food
  • The immune system produces an allergic antibody (IgE) to try to get the food out of the body
  • IgE can develop suddenly, even if the patient has eaten that food before in the past
  • Symptoms can be quite severe with a rapid onset and in some cases life-threatening
  • Food allergies are diagnosed via skin prick testing for IgE.
  • Children with true food allergies will be issued with an Epipen and carers trained on how to use it
  • It is possible to outgrow food allergies and intolerances with eggs and milk being the commonest. Peanut and shellfish allergies tend to be lifelong


Food Intolerances


  • The immune system is not driving the response
  • The problem is in digesting the food
  • The reaction can be quite delayed and comes on gradually
  • The response is not dangerous like an allergic reaction
  • Symptoms usually involve bloating, tummy pain, diarrhoea, eczema
  • May not occur if only small amounts of the food are eaten
  • Is not life-threatening

The key take-home message for parents is to always consult with your family doctor first who will be able to refer you and your child to an Allergy Specialist and Dietician who will be able to accurately test for and prescribe an appropriate diet if necessary. Your child ultimately needs a balanced, nutritional diet to grow and develop normally and dangerous food-exclusion can cause malnutrition and health problems.