Allergy or intolerance?

What is the difference between food allergy and food intolerance?

food intolerance infographicWhen someone has a food allergy, their immune system wrongly sees the food as hostile and the body's defence mechanism springs into action. This produces a range of symptoms which can vary from mild itching to severe breathing difficulties or even shock. These symptoms usually happen immediately after eating the food.  

When someone is intolerant to a food, the immune system is usually not involved and symptoms take much longer to develop and are generally not life-threatening. However, a food intolerance can adversely affect long-term health.


Are food allergy and intolerance forms of food poisoning?

No. In a case of food poisoning, someone has become ill due to eating a food that is contaminated with harmful bacteria or toxins. Contaminated food should not be eaten by anyone. With a food allergy or intolerance, the offending food is safe to eat for the majority of people. However, it triggers an unhealthy reaction in some people. For example, peanuts are nutritious and tasty foods enjoyed by a great many people but for someone with a peanut allergy they can be very dangerous.

How do I know if I have a food allergy or food intolerance?

It is very important that a food hypersensitivity (food allergy, food intolerance or coeliac disease) – is diagnosed medically. Self-diagnosis is extremely risky as many of the symptoms associated with these conditions are common to a number of other illnesses. It is important to remember that food poisoning from eating contaminated food, and food aversion – where someone just doesn’t like a particular food (but will not be ill if they eat it) – are not food hypersensitivities.

If you diagnose yourself, you may cut out of your diet certain foods that are safe and nutritious while at the same time continuing to include foods that may be risky. If you think you have a food hypersensitivity, you need to talk to your General Practitioner.

What happens in an allergic reaction?

Essentially, when the immune system reacts to a food ingredient during an allergic reaction, it triggers the release of chemicals such as histamine from cells in the body. This causes some or all of the following symptoms:

  • itching or swelling in the mouth and throat
  • hives anywhere on the body
  • runny nose and eyes
  • reddening of the skin
  • feeling sick
  • diarrhoea and/or vomiting

If the reaction is severe, other symptoms can occur including:

  • a sudden feeling of weakness (caused by a drop in blood pressure)
  • breathing problems (your throat might start to swell up or close)

This is an anaphylactic reaction, also known as anaphylactic shock, and is life threatening. It requires immediate treatment by adrenaline injection followed by expert medical assistance. Usually the symptoms happen within seconds or minutes of being exposed to the food but the reaction can be delayed for several hours. See the medical information section for more information.

What are the symptoms of an intolerance to a food?

The symptoms of an intolerance to food include those of an upset digestion – diarrhoea, bloating, upset stomach, etc. Weight loss, lethargy or anaemia can occur as well as migraine headaches and psychological effects such as confusion and even depression. However, these usually manifest over longer periods of time as well as a variety of other symptoms that can result from poor nutrition. In some cases the symptoms of a food intolerance resemble those of a mild allergic reaction.

Many of the symptoms of a food intolerance are also associated with other disorders of the digestive system such as Crohn’s disease and Irritable Bowel Syndrome.

What foods cause an allergic reaction?

Although peanut and nut allergies are probably best known due to the many media reports into related fatalities, any food can cause an allergic response in a susceptible person. To date, allergies to over 180 foods have been documented worldwide. Most of these are very rare and some are associated with particular populations or regions of the world. Cod fish allergy is common in Scandinavia, as is rice allergy in China and celery allergy in France. These allergies are less common on the island of Ireland where, like other Western countries, the more frequently encountered allergies include those to peanuts, tree nuts, egg, crustaceans, milk and wheat.

What foods can people be intolerant to?

There is also a wide variety of foods associated with food intolerance. The most frequently encountered in an island of Ireland context include milk (lactose intolerance) and gluten (coeliac disease; wheat intolerance) but also certain food additives such as monosodium glutamate (MSG). 

  • A person with lactose intolerance cannot digest milk properly (lactose is a milk sugar). Lactose cannot be absorbed by the body resulting in symptoms such as cramps and diarrhoea. For more on lactose intolerance see the‚Äč medical information section.
  • A person with coeliac disease reacts to gluten which is a protein found in foods such as wheat, rye, barley and oats. This results in damage to the gut with effects on nutritional status and general wellbeing.
  • Some people have reported symptoms such as flushing, temperature increase and headache after eating the flavour enhancer MSG. These symptoms are also known as “Chinese Restaurant Syndrome”, related to the fact that MSG is a frequent ingredient in many Chinese dishes. 

Other foods to which susceptible people are known to react include red wine, cheese, caffeine and salicylates which are found in certain vegetables, herbs, spices, fruits and chocolate.

Can you be allergic or intolerant to more than one food?

It is possible to have allergies to more than one thing. It is also possible to be intolerant to certain things and allergic to other things. It all depends on how similar the offending chemicals are in the food or pollen or whatever material you are allergic to. This is called cross-reactivity: if you have an allergy to a food, you can react to another substance (not necessarily another food) if it contains a protein like the protein that causes your allergy in the first place. 

  • For example, cross-reactivity may result in someone who is allergic to prawns also being allergic to shrimps, crab and lobster.
  • Quite often peanut allergic people are also allergic to lupin flour. 
  • Hen’s egg is cross-reactive with other eggs and cow’s milk is cross-reactive with milk from goats and sheep. 
  • Someone with a wheat allergy can also be allergic to rye and grass pollen. 
  • Some cross reactions are less obvious: an allergy to house dust mites may lead to an allergy to shellfish (molluscs and crustaceans) while an allergy to latex rubber increases your risk of becoming allergic to certain fruits and vegetables. 
  • Those who are allergic to pollen, particularly birch or olive pollen, may develop allergic symptoms when they eat hazelnuts, apple, cherries, pears or carrots. 

How can I find out if a food product is being withdrawn or recalled for food allergy reasons?

When allergy labelling is incorrect or inadequate or if there is another reason which puts food allergy sufferers at risk, the food product has to be withdrawn or recalled to protect consumers who can stay informed about the latest withdrawals or recalls by signing up for food allergy alerts by email or SMS text message.

These alerts are issued regarding the possible risk to food hypersensitive consumers from a particular food. In the Republic of Ireland, consumers can subscribe to the Food Safety Authority of Ireland (FSAI) allergen alerts. In Northern Ireland, consumers can subscribe to allergen alerts from the Food Standards Agency (FSA):

Are there any support groups or organisations for people with food allergy or intolerance?

Yes. In the Republic of Ireland, the Irish Anaphylaxis Campaign works to raise awareness of the condition and to provide support to those at risk to potentially fatal food allergies. For people with coeliac condition, support can be obtained from The Coeliac Society of Ireland and Gluten-Free Ireland in the Republic of Ireland or Coeliac UK in Northern Ireland.