What is the difference between food allergy and food intolerance?

What is a food allergy? 

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, eczema, chronic diarrhoea and poor growth in babies or children. Researchers have found that up to 40–50% of eczema in young children is triggered by food allergy.  

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

Food allergy affects up to 10% of babies, 6% of children and 2% of adults.  

Read more about food allergies.  

What is a food intolerance?

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.  

What is the difference between food allergy and food intolerance?  

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

How are food allergy and food intolerance diagnosed?

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.

Can I prevent my child getting a food allergy?  

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.  

Learn more

What is the difference between a food allergy and a food intolerance? Allergy NZ

Reviewed by

	Dr Alice Miller trained as a GP in the UK and has been working in New Zealand since 2013. She has undertaken extra study in diabetes, sexual and reproductive healthcare, and skin cancer medicine. Alice has a special interest in preventative health and self-care, which she is building on by studying for the Diploma of Public Health with the University of Otago in Wellington.