What's the difference between food allergy and food intolerance?

A food allergy is an exaggerated immune system response to a food protein. When you eat this protein, your body triggers an allergic reaction. Symptoms can include hives, itching, swelling, vomiting, diarrhoea (runny poos) and nausea (being sick).   

In some cases, it can cause potentially life-threatening symptoms, either breathing difficulties and/or a sudden drop in blood pressure. This is called anaphylaxis.   

Sometimes food allergy may be less obvious. Signs can include infant colic, acid reflux, chronic diarrhoea and poor growth in babies or children. Food allergies don't usually cause eczema symptoms.

Eight foods cause 90% of allergies: milk, egg, peanuts, tree nuts, fish, shellfish, wheat and soy. However, any food can cause an allergic reaction. 

Image credit: Canva 

Food allergy affects up to 10% of babies, 6% of children and 2% of adults.  Read more about food allergies. 

People with eczema often have other allergic conditions, including food allergy, but food allergy does not cause eczema. Food allergy is more common in infants with eczema and a family history of allergy. Around 30% of infants in these groups develop food allergy compared to only 10% in the general population. There is some evidence that managing eczema well during infancy may reduce the chance of an infant developing food allergy.

When a child has eczema and food allergy, food allergy may trigger eczema, but it isn't the cause of their eczema. Most food allergy causes hives, vomiting and irritability within 30 minutes of eating. Food allergy only occasionally results in delayed eczema flare ups.

Skin tests

Results of skin tests or blood tests for food allergy do not predict food/s that are making the eczema worse. Allergy testing should only be done if it is recommended and interpreted by a clinical immunology/allergy specialist.

Excluding foods

Excluding some food from your child’s diet should only be tried when eczema doesn't improve with regular eczema treatments. Confirming that food allergy is causing delayed eczema only requires excluding food for a short term. This trial should always be supervised by a clinical immunology/allergy specialist. If the specialist recommends continuing food exclusion longer term, children should also see a paediatric dietitian with specialised knowledge of food allergies.

Taking foods out of a child’s diet without using the right substitutes can cause malnutrition and poor growth. If a child has been regularly eating a food without signs of allergy, taking that food out of their diet can result in them developing a new allergy to that food.

Many people think they are allergic to a food when in fact they have an intolerance to the food. A food intolerance is an unpleasant reaction to a food, but the reaction does not involve your immune system. Reactions can happen straight after eating a food or up to 20 hours later.  

Symptoms of intolerance are uncomfortable but not life-threatening. They can sometimes be vague and include a combination of the following: gastrointestinal problems such as bloating, wind, diarrhoea, nausea, indigestion, eczema or asthma getting worse.   

Food intolerances can sometimes have the same symptoms as other health conditions, so if you have these symptoms see your doctor. They can rule out other conditions.  

Common food intolerances are lactose intolerance, which means you can’t digest the sugar found in dairy products, and gluten intolerance, also known as non-coeliac gluten sensitivity. This is different from coeliac disease, an autoimmune disorder in which your immune system reacts to gluten. The immune reaction in coeliac disease is not as severe as a food allergy, although it can damage your gut and lead to other health complications over time. This is why people with coeliac disease must avoid even tiny amounts of gluten, whereas people with gluten intolerance may be able to eat it in small amounts or occasionally.

Irritable bowel syndrome (IBS) may be a sign of an intolerance to foods that are high in a type of short-chain sugar. These foods are known as FODMAPs. Read more about IBS and FODMAPs.

To learn more about the difference between food allergy or intolerance, read cows’ milk allergy or intolerance? 

Your GP will ask questions about your symptoms, including when and how often they occur. If the symptoms are consistent with being a food allergic reaction and appear within a few minutes the first time of eating a particular food, then diagnosis of a food allergy is likely to be straightforward. However, your GP may refer you for a skin prick or blood tests to confirm the allergen concerned. If a food allergy is suspected or confirmed, you should be referred to a specialist for further tests and ongoing monitoring. This may include an oral food challenge. If a particular food allergy is suspected or confirmed, you should not eat the food until cleared by your specialist to re-introduce it to your diet.

Food intolerance is more difficult to diagnose as there are no tests. You may be asked to keep a food and symptoms diary to check for patterns. You may also be referred to a dietitian. The dietitian may suggest a short-term elimination diet.

There are some things you can do that may help prevent your child developing a food allergy. These include: 

• if you are pregnant or breastfeeding, include foods (the ones that can cause allergic reactions) in what you regularly eat 
• breastfeed if you can  
• introduce solid food at around 6 months of age 
• give your child to a variety of foods to eat
• see your doctor if your child has a reaction to a food.  

Read more about reducing food allergies in infants.