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

A food allergy is an exaggerated immune system response to certain types of protein in food. It's also known as an IgE mediated food allergy. When you eat or drink anything that contains the protein, your body triggers an allergic reaction. Mild to moderate reactions include skin hives/welts, swelling of your lips, face and eyes, stomach pain or vomiting (being sick).   

A severe allergic reaction to an allergen may include noisy breathing, swelling of the tongue or throat, difficulty talking, dizziness, loss of consciousness or collapse. This is called anaphylaxis and is a medical emergency – call 111 for an ambulance and give adrenaline (epinephrine) if it's available. 

Although almost any food can cause an allergic reaction, the main foods causing food allergy in Aotearoa New Zealand are dairy (cow's milk), wheat, egg, fish, peanuts, sesame, shellfish (crustacea and molluscs), soy, tree nuts (almonds, brazil nuts, cashews, hazelnuts, macadamias, pecans, pine nuts, pistachios, walnuts) and kiwifruit.

Image credit: Healthify He Puna Waiora

Food allergy affects about 10% of babies, 6 to 8% of school-age children and 2 to 4% of adults. Read more about food allergies. 

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, and may involve parts of your immune system. It's also known as a non-IgE mediated food allergy. Reactions can happen straight after eating a food or days later.  

Food intolerances may include:

• Issues digesting certain foods, such as:
  • lactose intolerance where your body can’t digest the sugar in milk
  • gluten intolerance (also known as non-coeliac gluten sensitivity)
  • intolerance to certain short-chain carbohydrates in foods called FODMAPs.
• Sensitivities to chemicals in food such as caffeine, monosodium glutamate (MSG) and other naturally occurring chemicals (eg, salicylates and amines).
• Adverse reactions to artificial preservatives such as sulphites and benzoates.

Symptoms caused by food intolerance are uncomfortable but not life-threatening and can affect your:

• gut causing bloating, gas/flatulence, irritable bowel syndrome (IBS), diarrhoea, constipation and stomach pain
• nervous system causing headaches, migraines, and fatigue
• skin causing rashes, eczema, hives (urticaria), swellings and mouth ulcers
• airways causing an itchy, runny nose and increased mucus in your sinuses.

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

Food allergy

• What it is: When a person’s immune system overreacts to a protein in food and they experience an allergic reaction.
• Reactions: Immediate within minutes to 2 hours. 
• Symptoms: May include
  • tingling or itching in your mouth
  • itchy red rash
  • swelling of your face, mouth, throat or other areas of your body
  • difficulty swallowing
  • wheezing or shortness of breath
  • feeling sick or vomiting
  • abdominal (tummy) pain or diarrhoea (runny poos)
  • hay fever-like symptoms, such as sneezing or itchy eyes.

Some people may develop a severe allergic reaction (anaphylaxis), which is life-threatening and a medical emergency

• Age of onset: Most common in young children less than 5 years of age. 
  
• Triggers: Specific food proteins (egg, milk, peanut, tree nuts, sesame, fish, crustacean etc).
  
• Dietary management: Completely avoiding the food(s).
  
• Outcome: Egg and milk allergies are usually outgrown, peanut, tree nut and seafood allergies often persist.

Food intolerance

• What it is: A bad reaction to a food or drink that doesn't involve your immune system. It may affect your digestive system, nervous system, skin or airways. 
• Reactions: Straight away, within a few hours or days later.
• Symptoms: May include:
  • hives/welts
  • bloating and wind
  • nausea (feeling sick)
  • diarrhoea (runny poos)
  • constipation
  • reflux
  • indigestion
  • migraine
  • abdominal (tummy) pain
  • sinus congestion.
    
    
• Age of onset: Any age.
• Triggers: Examples include lactose, FODMAP carbohydrates, sulphites, amines, salicylates, MSG.
• Dietary management: Exclusion, some people can tolerate a small amount of the food. 

There are other immune-related reactions to food which are usually delayed and related the digestive system (gut).

These include:

• Food protein induced enterocolitis syndrome (FPIES) which mainly affects babies and young children. Symptoms (extreme vomiting and diarrhoea) are delayed and usually occur 2 to 4 hours after the food has been ingested. Some children can go into shock and need emergency treatment. The main food triggers are rice, cow’s milk and soy, but any food can cause an FPIES reaction.
• Food protein-induced allergic proctocolitis (FPIAP) which usually first occurs in babies during their first few months of life. Symptoms include blood in the stool (poo) and sometimes mucus. Symptoms occur within 72 hours of ingesting the food. The main triggers are cow’s milk (through breast milk) and occasionally soy.
• Oral allergy syndrome (OAS) is caused by the immune system in someone with an allergy to a pollen, mistaking protein in the pollen with a similar protein in some fruit, vegetables and nuts. This is known as cross-reactivity. Symptoms include itching or swelling of the lips, tongue, throat or roof of your mouth. Anaphylaxis is very rare.
• Coeliac disease is caused by an immune system response to foods containing gluten. When gluten-containing cereals (eg, wheat, barley, rye) are eaten, it leads to inflammation of the gut which results in poor absorption of nutrients. Major symptoms are gut upset, fatigue, anaemia or weight loss. This is a life-long condition which must be treated with a gluten-free diet. Read more about coeliac disease. 

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

Your healthcare provider will ask questions about your symptoms, including when and how often they occur.

Food allergy

If the symptoms are consistent with being a food allergic reaction, and appear within a few minutes of the first time a particular food is eaten, then diagnosis of a food allergy is likely to be straightforward. However, your healthcare provider 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 an allergy specialist and allergy dietitian for further tests and ongoing monitoring. This may include an oral food challenge. If a particular food allergy is suspected or confirmed, you shouldn't eat the food until your specialist has advised you to re-introduce it to your diet.

Food intolerance

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.

You should always see a paediatric or allergy dietitian before removing any food groups (eg, dairy or wheat) from your, or your child's, diet unless there has been an immediate reaction to the food. Any avoidance of foods needs to happen with medical and dietitian supervision to make sure there's adequate nutrition for growth and development.

Be careful of non-evidence based tests

There are a number of tests (eg, hair analysis, saliva testing and vega testing) that are not scientifically proven or reliable for diagnosing allergies. The results of these tests can be incorrect, leading to misdiagnosis and the unnecessary restriction of foods. 

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

These include: 

• If you're pregnant or breastfeeding, eat a healthy balanced diet rich in fibre, vegetables and fruit. Include foods (the ones that can cause allergic reactions) in what you regularly eat.
• Breastfeed if you can for as long as you are able to. There is some evidence showing that breastfeeding during the period that solids are introduced to infants from around 6 months may help to prevent food allergy.
• Introduce solid food at about 6 months of age.
• Give your baby a wide variety of foods including peanut butter, cooked egg, dairy and wheat products in the first year of life. This includes babies at high risk of allergy. if your baby or child has an allergic reaction to a food, stop giving that food and seek medical advice. 

Note: Hydrolysed (partially and extensively) infant formula is not recommended for the prevention of food allergy. Read more about infant formulas and reducing food allergies in infants.

Eczema and food allergy

Eczema is a skin condition which affects about 1 in 5 babies and young children. It affects their skin causing redness, itching and sometimes infections.

Eczema is more likely to develop in people with a family history of allergy, and it's common for people with eczema to have other allergies. Studies have shown that up to 30% of babies with eczema, with a family history of allergy, will develop food allergy.

For some babies with severe eczema and food allergy, short term removal of certain food/s using a medically supervised elimination diet may result in better eczema control:

• If their skin improves, foods are gradually re-introduced, one by one, in a medically supervised food challenge. This will help identify which food is causing the eczema to flare.
• If there's no improvement after 2 weeks of the elimination diet, it's unlikely that food allergy is the cause of eczema.
• If food allergy isn't the cause of eczema, removing foods won't reduce symptoms.

Elimination diets and food challenges should always be supervised by medical specialists trained in food allergy alongside a specialist allergy dietitian. Unnecessary removal of foods from a child’s diet can affect their growth and development. It can also increase the risk of developing allergy to those foods.

Read more about eczema for young adults with food allergy(external link).