To learn about the characteristics of lactose and allergies, see the previous entry – Lactose Intolerance or Allergy.

Updated article : October, 2023.

Allergy to a food

We talk about food allergies when there is an inadequate and excessive immune response following contact (by eating it) with an ingredient in a food (often proteins), which then repeats each time the food is consumed.

When a baby shows an allergy to a food, it is their immune system (the body’s defence mechanism which can be identified by IgE-mediated) that starts up. It is activated to fight an undesirable invader contained in this food and provokes a moderate to severe reaction each time the food is ingested. At the start, in a young baby, the reaction can be progressive during repeated contact with the allergen. The signs will be more automatic after a certain time. A mixed allergy can also be identified, with additional clinical signs such as skin reaction (e.g. eczema), esophagitis or gastritis (inflammation of the esophagus and/or stomach in response to allergen absorption).

A milk allergy is without a doubt more frequent in a baby as milk protein is the first given to a newborn and affects 2.5% of them.

In the case of a milk allergy, you can observe the appearance of symptoms in a couple of minutes up to 2 hours, and the reaction will last a couple of hours or less.

Given there is a freeing of antibodies in the blood circulation when there is an allergy, we can diagnose more severe allergies, called IgE-mediated, by a blood test, a skin test (Pick test or with a stamp) and also with an oral provocation test. For the oral provocation test, it is usually done in the hospital supervised by a medical team in order to react quickly after the allergen food is ingested and document the reaction of the child in a controlled setting.

When we talk about serious allergies to a food with an anaphylactic type response (immediate hypersensitivity), the reaction can be almost automatic, within the minutes or two hours that normally follow the ingestion and sometimes contact with the food. The evolution remains unpredictable. The reactions can be gastro-intestinal, mouth, respiratory tract, cardiovascular system, central nervous system, eyes and skin in 80-90% of cases. They can be very severe and place the child’s life in danger. Avoidance and an epinephrine self-injector are the treatments based on the child’s age.

Food intolerance

Intolerance (also called IgE-non-mediated type allergy or without medication) leads to discomfort or gastro-intestinal symptoms and occur after the ingestion of certain foods with variable intensity (discomfort, diarrhea, constipation, irritability, mucus). These reactions are increasing in babies and remain irritating as there are no tests to diagnose an intolerance. Most of the time, digestive symptoms that lead us to this conclusion, even if the skin and respiratory system can also be affected. For very young children, intolerance to cow milk proteins is without a doubt the most frequent as it is the first foreign protein introduced to the newborn’s diet.

An intolerance does not provoke the baby’s immune system like a severe allergy, and there is no anaphylactic shock. But the intolerance can provoke an inflammatory reaction in the intestines within hours or days follow exposure and also lead to discomfort in the baby.

An intolerance can sometimes affect only the large intestine (distal colon), a situation that often occurs in the first 4 to 6 weeks of a baby’s life. This is considered the least severe form of intolerance. In a certain number of children, intolerance will continue to progress towards the small intestine, and in the worst case, affect the entire digestive system, from the esophagus to the anus. In the case of intolerance, the baby has no growth problems, gains weight adequately and is generally healthy.

The intolerance cannot be detected in blood or by skin tests as there are no antibodies circulating due to a case of an intolerance. This is why we would try to find the food that seems to create the undesired reactions in the baby a try to eliminate it from the breastfeeding mother with an elimination or exclusion diet. If the baby drink commercial formulas, you have to adjust the formula with proteins partially or strongly hydrolysed to help the baby digest and absorb. After 2-4 weeks will we see if the situation seems to improve or not for the baby. For a breastfeeding mother, it is useless to remove too many things at a time and deprive the mother of foods that do not affect the baby. For the baby, start by eliminating milk given that milk proteins are the most frequent allergen, then, if only necessary, soya then beef. Next, we’ll eliminate soy (if necessary), then eggs, and if necessary (in very rare cases) we’ll remove wheat, corn and beef.

If the baby’s reaction to cow milk protein is rather slight (discomfort is present, without other major symptoms), the simple fact of diminishing daily milk sources in the breastfeeding mother will improve the situation, above all if the mother consumes too many portions of dairy products in a day (recommended 3-4).

If the baby’s reaction to cow milk proteins is rather severe (vomiting, blood in stools, severe diarrhea, dermatitis, breathing difficulties or generalized urticaria), the exclusion diet for the mother will be stricter and requires the elimination of all sources of milk, even trace, in many products sold and consumed in our everyday diet – cereal, bread, soup, sauces, candy, vinaigrettes, etc.

You should almost always start by removing all sources of cow milk protein (milk, cream, cheese, yogurt), because it is the most extensive allergen in Canada. If you do not note a change, you have to examine what other food could cause reactions in the baby and eliminate it for at least 7-10 days because normally it takes 3-6 days to completely remove the cow milk proteins from breastmilk.

To gradually reintroduce traces of bovine protein via dairy products into the diet of a breast-feeding mother who has been on the avoidance diet for at least 3 months, ideally you should wait until the baby is over 6 months old before attempting to reintroduce the allergen, and then only if there have been no significant symptoms for 3 weeks. If symptoms recur, wait another 3 to 4 weeks before attempting to reintroduce the food (12 months if the baby is very fragile or born prematurely).

It is never advisable to restrict the diet of a new breast-feeding mother as a preventive measure, even if there is a history of intolerances or allergies among siblings.  Avoiding food puts the child at even greater risk over time.

Here’s a useful tool for all moms on an eviction diet, made by Allergie Québec (in french only).

In Canada, we often noted crossed allergies, like goat and sheep milk at 90%, soya 10-15%, beef 10% and other rarer allergies, such as oats, eggs and other grains (barley, corn and wheat), a vegetable (ex.: avocado), other meats and fish are other possible allergens, in order of importance. In Australia, rice is the larges allergen, and in the US soya.

In the case of more serious reactions, it is often advised to see a nutritionist that specialises in pediatrics, or even an allergist if needed.

Food journal

It is a good idea to keep a food journal to follow up with a nutritionist, doctor or allergist. If a baby reacts to an allergen, they could be more likely to react to other sources of nutrients with an allergen potential, like a different cereal for example (other grain, reaction).

This is why when we introduce solid foods for a baby that shows intolerance or allergies in the first months of like, we suggest slowly introducing new foods while not delaying them. You should start with vegetables and fruits that have a lower risk of reaction, and then add meats (never before 6 months of age) and cereals later. It is good to follow up with a nutritionist to see changes in the situation, a follow up for the growth of your baby over time with the addition of foods and their reactions. Parents need to be guided to know when to reintroduce milk proteins in the baby’s diet, and that can easily be around 9-12 months.

At the start, when the baby’s reaction to an allergen is slight and the baby’s condition has really improved with an elimination diet for the breastfeeding mother, try later, after the baby reaches six months, and reintroduce the food allergen in the mother’s diet (like traces of milk protein). You will try to note if the baby’s reactions reappear or not.

This is like an oral provocation. We note if the child, despite the fact that their digestive tube as matured at around 9 months, remains fragile vis-à-vis the cow milk protein. If the reaction returns, the food is stopped again and the allergen can be reintroduced after the baby has been symptom-free for 3 weeks. If the baby’s reaction was severe, wait until after 1 year of age or even more depending on the case, with directions from an allergist. We will go very gradually. On the scale of reintroducing milk proteins, you can start with traces of milk in a cooked recipe, such as muffins or cookies. Next, a recipe with more milk, such as in pancakes or omelet, and gradually, if the breastfed baby is still symptom-free, we can move on to cheese on pizza and finish with milk to drink or with a portion of yogurt, ice cream or cheese.

When certain foods and allergens are introduced, a child may react more intensely and develop enterocolitis syndrome. This is induced by food proteins, also known as SEIPA. In fact, this syndrome refers to an inflammation of the mucous membrane of the small and large intestine (the colon), and when the system reacts to a food, in this case, it’s a reaction of the child’s immune system. In this syndrome, vomiting and/or diarrhea often occur 2 to 3 hours after ingestion of the food concerned and can lead to severe dehydration and complications for the child. Dairy products and soy are the two allergens most associated with SEIPA. Sporadic follow-up with an allergist and nutritionist is advisable, and in most children, the syndrome resolves spontaneously before school age.

For babies that receive commercial formula and react to it, you have to document their medical history and then see if a milk that is easier to digest can be suggested if necessary.

5% of newborns manifest allergic reactions compared to 3-4% of adults. A high number of food allergies diagnosed before 3 years of age will disappear over time.

To continue reading, go to the next entry – Origins of Food Allergies.