Food Allergy

Food Allergy occurs when your immune system overreacts to a food by mistakenly labelling it as a threat and triggering an immune response. The symptoms resulting from this immune response are often mild but they can also be very serious and trigger a life threatening reaction known as anaphylaxis

Symptoms of Food Allergy

The symptoms of food allergy may involve the skin, airways and digestive tract. The most common symptoms are:

  • red raised itchy rash or hives (urticaria)
  • itchy sensation inside the mouth, throat or ears
  • swelling of the lips, eyes, tongue or mouth (angioedema)
  • vomiting

In the most serious cases, a person has a severe allergic reaction (anaphylaxis), which can be life threatening. The symptoms of anaphylaxis include:

  • breathing difficulties
  • trouble swallowing
  • feeling faint or lightheaded

Common Food Allergies

An allergic reaction can be caused by almost any food but certain foods are responsible for the majority of food allergies.

The foods that most commonly cause an allergic reaction are:

  • milk
  • eggs
  • nuts
  • fish and shellfish
  • certain fruit and vegetables

Causes of Food Allergy

Although it is not well understood as to why people develop allergies to food, it is clear that they often have other allergic conditions such as asthma, hay fever and eczema.

Most children that have a food allergy will have had eczema during infancy. When a child's eczema begins at an earlier age and is more severe they are at increased risk of developing food allergy.

It is known that introducing nuts to your childs diet early (from age 7 months) reduces the risk of developing a nut allergy. 

Types of Food allergies

Food allergies are divided into 3 types:

  • IgE mediated: This is the most common type and is triggered by the immune system producing an antibody called immunoglobulin E (IgE) in response to a specific food. Symptoms occur within 30 minutes of eating. Anaphylaxis is most commonly associated with this type of allergy.
  • Non IgE mediated: These allergic reactions are caused by other components of the immune system rather than IgE. This type of allergy is more difficult to diagnose as reactions do not occur immediately after the ingestion of the food. The symptoms are often gastrointestinal such as vomiting, bloating and diarrhoea. 
  • Mixed IgE and non-IgE mediated: Some food allergies occur through both of the above mechanisms.

Food Allergy and Eczema

People who have eczema with elevated IgE levels are more likely to have food allergies and airborne allergies. Current research indicates that skin barrier defects found in eczema alter immune function and can induce food allergy secondarily. Primary sensitisation is more likely to occur when new allergens are introduced through inflammed eczematous skin rather than the gastrointestinal tract. It is therefore important that parents avoid introducing new foods, especially nuts and shellfish, during any acute exacerbation of eczema in infancy.


  • Avoidence: The best way to prevent an allergic reaction to food is to identify the culprit and avoid it. Ensure that your speak with your GP first before cutting out any foods from your or your child's diet.
  • Mild - Moderate Allergic Reactions: Antihistamines can help relieve mild symptoms.
  • Severe Allergic Reactions / Anaphylaxis: Adrenaline is the primary treatment used in these cases. e.g Epipen

Food Allergy Testing

If you think you or your child has a food allergy make sure you have this confirmed by allergy testing. It is important that the results are interpreted by a specialist medical doctor.

Perform an allergy test is easy, the skill lies in interpreting the result in the context of the patient's symptoms. Sometimes there is no link between the suspected allergen and the symptoms. As the case study below explains, trying to be your own detective can be misleading and take you along the wrong path and away from recovery.

Case Study

Jennifer is a nineteen-year-old student.  She did exceptionally well in her final state examinations and now studies law in Dublin.  Jennifer also has recurring sinusitis with impaired senses of smell and taste.  Jennifer grew up in a small country along the south coast of Ireland.  Before moving to university she lived at home with her parents and had a healthy diet with mainly home-cooked food.  But everything home cooked tasted rather bland and Jennifer kept asking for something with a bit of spice in her food.  But mother refused.  She preferred good, wholesome produce.  She rarely used tins, packets, bottles or artificial stock cubes when preparing dinner.  So Jennifer’s wish for spice went un-satisfied.

Once Jennifer left to continue her studies she started to lead her own life, away from the constraints of her parents.  She preferred the city night lights to the college library.  She wanted experiences far removed from small town Ireland.  And she didn’t want to waste time cooking.  So she ate out a lot, or bought in, or grabbed fast and easy to prefer foods.  Such as cardboard cup-in-soups, cardboard instant rice dishes, cardboard instant curries and pre-cooked spicy chicken wings.  The easier the food to prepare, the more attractive it was to Jennifer. And she enjoyed this produce better; she could actually taste something for a change. It at least had a tang to revitalize her jaded palate.

Unwittingly, Jennifer was swallowing a significant number of food additives.  The tang in her diet was created by chemicals, mainly Mono-sodium-glutamate (MSG, E-621). 

One evening she came out in a very itchy rash, hives as she recognised it.  The rash subsided with an antihistamine.  Then one evening her upper lips swelled, then the hives returned with a vengeance and it took days and a lot of antihistamines to calm her skin.  Finally, one evening after a Chinese meal, Jennifer’s lips, face and tongue swelled.  Her sinuses became inflamed, painful and congested.  The hives returned and this time didn’t go away, despite double the usual dosage of antihistamines. 

An ingredient in the Chinese meal was peanuts and Jennifer concluded she had become peanut-allergic.  And this frightened her because she knew that some people can get life threatening reactions if they have a strong allergy to peanuts.  So she went to an allergy centre to find out what was happening. 

Allergy testing showed Jennifer had strong dust mite and grass pollen allergies.  These were causing her sinus problems but certainly not her hives and facial swellings.  All of the foods tested did not provoke a positive response.  Conclusion: Jennifer’s allergic reactions were not due to a food allergy. “So what then”, asked Jennifer “could be causing this?” Fiberoptic inspection of her nasal cavity showed a grossly swollen nasal lining with fluid ‘blistering’ along the upper turbinates.  Left unchecked this would eventually trigger allergic nasal polyps.  More importantly, the swelling was interfering with the delicate nerve ending carrying the sensations of taste and smell to Jennifer’s brain.

It was explained that to get better she had to avoid specific E-numbers (the chemical additives put in certain food products to colour, flavour and preserve).  She would also start a treatment plan to restore her nose and sinuses to normal and recover the lost senses of taste and smell.  With full recovery she would enjoy good, wholesome food and not be so inclined to go for spice in her diet. 

Case history conclusion:

Jennifer wasn’t allergic to foods; she was allergic to chemicals in the food.  She can eat healthy, untainted-by-additives produce but has to avoid chemical enhanced foods and drinks.  Once she was allergy tested she had a clearer picture of her allergy issues.

When to seek medical advice

If you think you or your child may have a food allergy, it's very important to ask for a professional diagnosis from your GP. If appropriate, they can then recommend a reputable specialist allergy testing clinic such as Allergy Ireland for expert interpretation.

Many parents mistakenly assume their child has a food allergy when their symptoms are actually caused by a completely different condition.

Commercial allergy testing kits are available, but using them isn't recommended. Many kits are based on unsound scientific principles. Even if they are reliable, you should have the results looked at by a health professional.

Pollen Food Allergy Syndrome (PFAS)

PFAS is also known as Oral Allergy Syndrome and is caused by cross-reacting allergens found in both pollen and raw fruits, vegetables, or some tree nuts. The immune system mistakes pollen with similar appearing proteins in food and directs an allergic response against it. Some people experience itchiness in their mouth and throat, sometimes with mild swelling, immediately after eating fresh fruit or vegetables. Oral allergy syndrome generally doesn't cause severe symptoms and it is usually possible to deactivate the allergens by thoroughly cooking any fruit and vegetables. This changes the shape of the culrit proteins so that the immune system no longer recognises them.

Food labelling

Become a LABEL DETECTIVE when you buy food for your family. Labels and ingredient listings can change without warning. There is a risk of incorrect labelling of products with imported goods. Labelling mistakes can occur during translation.

  • Read all product labels every time you purchase a product. 
  • Check labelling on both outer and inner packages as discrepancies on food ingredient labelling can occur between the outer and inner packages in multi-packs.

FAQ's about Food Lists and "May contain" statements

I have heard that lists of "safe" products are not recommended. Why not?

Relying on a list of "safe" products is not recommended because ingredients and recipes can change without warning, thus making it impossible to keep an up-to-date list. Ingredients can sometimes vary depending on the product size (i.e. regular and mini), or manufacturing location. The safest policy is to read the ingredient statement for all products every time you make a purchase.

Lists are left in drawers and they do not encourage the food-allergic individual or their carers to always read the label.

Can products with "may contain" statements be consumed by those with food allergies?

It is not recommended, as this statement is there because the food manufacturer feels there could be a risk of contamination. Cross-contamination during food preparation, processing and packaging does occur and when a product is purchased the consumer has no real idea how great that risk may be. It is like "Russian Roulette", maybe the package bought last week was fine but the product bought this week "may contain" the specified allergen. It is safest to heed the warning on the product.

 "May contain…." can really contain.

Can products with "may contain" statements be consumed by non-allergic children in preschools and schools but still be around the children with food allergies?

Severe reactions usually occur when an allergic individual has consumed the allergen. It is recommended that food allergic individuals totally avoid the food they are allergic to.

It is reasonable for non-allergic children to consume foods that "May contain…"around the allergic person as long as there is adult supervision and strategies are in place to minimise the risk of a reaction, e.g. a "no food sharing" rule, hand-washing after eating, etc.

How can I find out if an allergen is present in a product, flavour or spice?

  • Call the manufacturer and ask if the allergen is present in the product, flavour/spice for that product.
  • If the manufacturer cannot answer your questions, you may have to avoid that product to be extra cautious about avoiding your allergen, particularly if there is a history of severe allergic reactions.

What should I do if I have a reaction to a product that should not have caused a reaction?

Do not discard the product as it may be needed for analysis. Wrap up the product and secure it in a location where it won't be accidentally eaten again. If it is perishable, store it in the freezer. Record any identifying product code information, place of purchase, date of purchase, etc.

  • Report the reaction to the manufacturer or the distributor if the product is made overseas.

How can I tell what a company's policy is regarding allergens?

  • Call or write to the manufacturer.
  • Some manufacturers list their policies regarding food allergen labelling on their websites.
  • Be specific. Tell the manufacturer which foods you are allergic to.
  • Phrase your questions so they can be answered with a "yes" or a "no" (e.g. "Does the flavouring in product X contain milk?").

Nut / Peanut allergies

The following foods can cause problems for the nut/peanut allergic person when eating out and should be avoided unless they can positively confirm there is no nut/peanut protein present:

  • Chinese and Thai dishes (even soup!)
  • Baked goods (pastries, cakes, biscuits, etc.)
  • Sauces (e.g. chilli sauces)
  • Desserts
  • Toppings and gravy. Peanut sauce has also been used as a secret ingredient for marinating chicken.

Avoiding all nuts

  • If you have a peanut allergy it's safer to avoid all nut products. Sometimes peanuts will be stored near other nuts in the production line or processed with other nuts, and contamination may occur as a result of this practice. Tree-nut allergic individuals should avoid peanuts for the same reasons.

Hidden egg and milk protein

Always be aware of foods that have a shine to them. Egg and milk can be used to give food this glazed appearance, e.g. bakery items.

Soy allergy

Fish sauce can be used as a substitute for soy sauce.

Food additive 322 - lecithin

Most commercial lecithin is obtained from soybeans. Other sources are egg yolks and leguminous seeds, including peanuts and maize.

Beware fresh food

Many butchers and fresh food outlets now have ready-to-cook products such as satay skewers or seasoned foods that contain egg and/or milk powder. These allergen-containing foods may very well be sitting next to the plain foods or prepared on the same surfaces etc. When buying fresh food (chicken, meats, etc.) be aware that shop assistants may have been handling foods that present a risk to your child. To be certain your food is not contaminated request that the shop assistant put on a clean pair of gloves. Also make certain the food you buy has not been lying beside foods that are likely to contaminate the food you are buying.

Hidden ingredients

  • Casein maybe used as a binder in meat products and "restructured" salmon or imitation seafood.
  • Worcestershire sauce may contain anchovies and/or soy.
  • Beware of bakeries - there is no labelling so you cannot be sure of content. Bakeries pose a high risk of contamination due to open displays, etc.

Trying a new medication or food

When giving a child a new food or medication, do so earlier in the day so you can keep an eye on your child.

Allergens in the house

It is much easier to manage life at home if the allergen is removed from your house; however, this is sometimes very difficult, especially in the case of egg and dairy, for example.

  • If you do have the allergen in your home, wash contaminated kitchen utensils separately in hot soapy water or in the dishwasher.
  • Use hot, soapy disposable paper towelling to wipe surfaces that have had the allergen on them. This allows removal of the allergen without contamination of the everyday sponge or washcloth.
  • Use separate sponges (colour coded) for washing up to reduce risk of cross contamination. Do not store sponges together.
  • Use a plastic basket in the fridge to contain allergic foods, e.g. milk, eggs, so the child knows not to touch the foods/products in the basket and can learn to recognise the products.
  • Use separate oil for cooking with risk foods.

Pet food

  • Fish food can trigger reactions in seafood-allergic people. Some fish food contains shrimp meat and other seafood.
  • Canned/dry pet food does contain allergens. Check labelling of your pet food.

Takeaway food and restaurants

  • Be aware of foods that are cooked in the same oil as risk foods (e.g. fish crumbed with egg, cooked in the same deep fryer as chips).

BBQ safety

  • If you are having a BBQ away from home cook your child's food on foil to be sure no other food comes in contact with it.
  • Consider purchasing your own portable BBQ to ensure no allergen comes in contact with your child's food during cooking.

 Parties and Special Occasions

  • Keep suitable party cake slices individually wrapped and stored in the freezer. When you need to send the child to a party/special occasion/school celebrations etc., you can choose a piece from the freezer. Try to be prepared for the unexpected "special" occasion - keep frozen, labelled treats in freezer at home/school for treats/birthdays.
  • Special occasions and celebrations constitute increased risk for food anaphylactic individuals. There is an increase in food consumption and away from home activities. Be aware that with all the rush and excitement of social gatherings, others may forget about your special food needs.
  • Be prepared to take extra precautions with checking foods offered or placed within reach of your child.
  • Christmas/Easter presents may need to be double-checked for that little packet of "goodies" that has no ingredient label.
  • Consider agreeing to take turns caring for your child while at social occasions. This will help give both parents a chance to socialise and relax with friends and family, knowing that their child is safe.

Visiting farms/ animals, parks etc.

  • Always check the contents of animal feed for allergens, especially if your child is hand-feeding animals, e.g. peanut has been found in cow feed and bird feed.
  • Activities at farms may include collecting eggs and milking cows. If your child is milk or egg allergic try to organise a different fun activity.


1. NHS: Food Allergy

2. Royal Children's Hospital, Melbourne: Food Allergy

3. The American College of Asthma, Allergy & Immunology: Food Allergy