What’s the Difference Between a Food Allergy and Food Sensitivity?

What’s the Difference Between a Food Allergy and Food Sensitivity?

Both food allergies and sensitivities (or intolerances) can have a significant impact a person’s quality of life, either through ongoing symptoms, the threat to life of having an allergic reaction or through the anxieties associated with reacting to foods eaten by mistake.

The main difference between these two reactions though is what is actually happening within the body.

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Food Allergies

Your immune system is your body’s defence against dangerous invaders like viruses and bacteria. When an allergic reaction takes place, the immune system mistakenly identifies a protein in a food you have consumed as a dangerous threat, and produces antibodies to fight it. The most common is called an immunoglobin E (IgE)-mediated reaction, which cause an immediate reaction releasing chemicals like histamine from mast cells. 

When someone has an allergy, even tiny amounts of an allergen could trigger a series of life-threatening reactions, known as anaphylaxis. Anaphylaxis requires immediate medical attention and should be treated as a medical emergency. Signs include skin reactions (itchy skin, a raised or red skin rash known as hives), swollen eyes, lips, hands or feet, swelling of the mouth, throat or tongue, which can cause breathing and swallowing difficulties, wheezing, feeling lightheaded or faint, collapse or unconsciousness, abdominal pain, nausea or vomiting.

There are also non-IgE-mediated food allergies, which are typically a more delayed reactions and occur primarily as digestive symptoms which could include vomiting, diarrhoea or bloating. Less is known about this type of reaction, but it is typically not life-threatening. It differs from other food sensitivities as there is no such thing as a ‘tolerance level’ when eating these foods as symptoms will come on after ingesting very small amounts.

14 Food Allergens 

There are 8 top food allergens which account for 90% of food reactions. These are milk, eggs, fish, shellfish/crustaceans (such as prawns, crabs and lobsters), peanuts, tree nuts (such as almonds, hazelnuts, walnuts, brazil nuts, cashews, pecans, pistachios and macadamia nuts), wheat/gluten and soybeans.

The other 10% of food allergic reactions are caused by these 6 food allergens: celery, lupin, molluscs (such as mussels and oysters), mustard, sesame, sulphur dioxide/sulphites.


Food sensitivities 

Food sensitivities will not trigger anaphylaxis and are not life-threatening. Where someone suffers with a food sensitivity, reactions will likely involve the digestive system as there is an inability or difficulty in processing or digesting a food. Common symptoms include gas, pain, bloating, diarrhoea, constipation or nausea. 

Food sensitivities and intolerances are more common than allergies and causes could include not having the right enzymes to digest a certain food, reactions to food additives or preservatives such as sulphites, MSG or artificial colours, sensitivity to caffeine or other chemicals, sensitivity to the sugars/carbohydrates naturally found in certain foods, poor gut health, suffering with IBS or other functional gastrointestinal disorders (FGIDs).



Food allergies can be diagnosed through a blood test, a patch or skin prick test, where the skin is exposed to allergens in the two latter tests, and is then observed for any visible reactions such as redness, itching or raised areas of skin. 

Other than with lactose intolerance where a breath test is available to measure amounts of hydrogen on the breath after drinking a lactose solution, there are no effective blood, hair sample, skin prick or other tests to diagnose food sensitivities. The only way to diagnose food sensitivities is through eliminating the suspected problem food from your diet for a period of days or weeks, testing if symptoms improve and then reintroducing the food.

Companies are increasingly bringing out tests that claim to diagnose up to hundreds of food intolerances at once but these are testing for raised levels of a substance called immunoglobin G (IgG), and there is no scientific evidence that levels of IgG increase after eating foods we are sensitive to. Levels can simply be high if it is a food we frequently eat and this does not mean we need to avoid it if we are having no symptoms! These tests can lead to misdiagnoses and unnecessarily restrictive diets, which can be harmful in the long term both in terms of our relationship with food and in terms of ensuring we get enough vitamins and minerals from our diet. 



Food allergies are lifelong conditions usually with no cure, but some babies and children do grow out of allergies over time. Where an allergy is really severe, you can be ‘desensitised’ to the allergen where you are exposed to it in very small amounts in a controlled environment by a medical professional. Otherwise, the only way to manage it is to avoid the allergen food for life.

With food sensitivities, where gut health is implicated in the cause, such as with IBS or other FGIDs, it can sometimes be the case that these food sensitivities can change depending on the balance of bacteria in our microbiomes. Where there is an imbalance, known as dysbiosis, symptoms can be worse and conversely, if our gut health improves, some people find so do their food sensitivities. It is sometimes the case that supplementing with digestive enzymes can help our bodies digest foods we would otherwise struggle to. This is not always the case however, and some food sensitivities are lifelong with no other treatment than to avoid the food for life. 



Food allergies and sensitivities are often confused, but the body’s reaction to each differs significantly as do the levels of danger they both pose to our health.  

Food allergies are very serious and can be life-threatening unlike food sensitivities, but both can lead to a significant impact on quality of life so it can be important to get to the bottom of these with the help of a health professional rather than trying to self-manage.


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This blog post was written by Jasmine Bliss, a Registered Associate Nutritionist (ANutr).