Food allergies are on the rise in infants. The heterogeneity of symptoms sometimes makes their diagnosis difficult. Once this has been established, an eviction regime will be put in place. The prognosis is most often favorable, with a natural evolution towards tolerance at school age.

Food allergy refers to the body’s abnormal reaction to a substance (here a food) usually tolerated by the majority of people.

There are two types of food allergy according to the underlying pathogenic mechanism:

Food allergy mediated by the presence of IgE antibodies (IgE-mediated):

Ingestion of the allergenic food induces an inflammatory response with the production of specific antibodies, immunoglobulins E (IgE). The reaction is then immediate. These forms, rare in infants, most often appear around 3 years of age.

Non-IgE mediated food allergy

Ingestion of the allergenic food causes the body to react via various symptoms, but there is no production of IgE. This type of allergy is generally expressed later. It is the most common form in infants.

Mixed forms.

Cow’s milk protein allergy (COPA) is the most common food allergy in infants, which makes sense since for the first 4-6 months, milk is the baby’s main food. With food diversification, other allergens appear. Eggs are commonly found allergens in infants, such as legumes, wheat, soy or fish. After 18 months, oilseeds (hazelnuts, walnuts, almonds) and peanuts can be responsible for food allergy.  

A family ground (parent, brother or sister with an allergy) predisposes to allergy. However, if allergies have a hereditary component, their transmission is not automatic. And vice versa: non-allergic parents can have an allergic child.

Symptoms of food allergy vary widely from child to child, depending on the underlying pathogenetic mechanism and the allergen involved.

In case of IgE-mediated food allergy

In case of IgE-mediated food allergy, it will be a food anaphylaxis. The symptoms are immediate, and can progress in different stages:

• stage 1: urticaria, pruritus
• stage 2: angioedema (swelling of the face), abdominal pain, nausea, vomiting
• stage 3: dyspnea, dysphagia, asthma attack
• stage 4: drop in blood pressure, loss of consciousness. It is anaphylactic shock, the most serious manifestation of allergy. Fortunately, it is rare in infants.

In infants

In infants, the non-IgE-mediated form is most common. The symptoms are mainly digestive and cutaneous:

• atopic eczema
• vomiting
• diarrhea
• reflux which can lead to esophagitis, with infant crying
• poor absorption of nutrients, and therefore growth retardation

In case of non-IgE-mediated food allergy 

Non-IgE-mediated food allergy can also lead to food protein enterocolitis syndrome (SEIPA).

• in its acute form, this syndrome will result 1 to 4 hours after ingestion of the food by strong vomiting, pallor, lethargy and sometimes, hypovolemic shock (drop in temperature, blood pressure, sometimes convulsions)
• in its chronic form, diarrhea and rectal bleeding which can be very severe, vomiting, growth retardation.

As these symptoms are not always specific, the non-IgE-mediated forms can initially be confused with infectious diseases with similar symptoms, or other diseases such as gastroesophageal reflux, common in infants.

The doctor will first carry out a clinical examination (skin, ENT, digestive and respiratory) and an examination of the nature of the symptoms, their frequency, the context of their appearance, the baby’s diet, the family history of allergy, etc. Tests will then be carried out.

For an IgE-dependent food allergy:

• a test skinprick. This skin test involves making a small amount of purified allergen extract penetrate the skin with a small lancet. 10 to 20 minutes later, the result is obtained. A positive test is manifested by a small pimple. Painless and safe, this test can be performed very early on in infants.
• a blood test for specific IgE 

For a food allergy not dependent on IgE:

• a patch test or patch test. Small cups containing the allergen are placed on the back. They are removed 48 hours later, and the result is obtained 24 hours later. Positive reactions range from a simple simple erythema to a combination of erythema, vesicles and bubbles. 

The definitive diagnosis is made by an eviction test (the allergen is eliminated from the diet) and oral challenge (it is reintroduced under surveillance to see the reaction).

To treat the symptoms caused by the allergy (especially hives), an antihistamine and sometimes corticosteroids may be prescribed. In case of risk of anaphylactic shock, an emergency kit (with an epinephrine auto-injector pen) for the home and for the nursery or school will be prescribed.

Once the diagnosis of the allergy has been made and the allergen clearly identified, the treatment is based on the total elimination of the food in the child’s diet. For processed foods, it is therefore necessary to carefully check the labels. The 13 most common food allergens must be included.

The natural course of food allergy in infants changes more or less favorably depending on the allergen in question. APLV is an allergy with a good prognosis: in the majority of children, it naturally evolves towards the development of tolerance, and milk can then be gradually reintroduced into the child’s diet. Egg, soy and wheat allergy also has a favorable prognosis, resolving before school age in most cases. Conversely, allergy to fish, shellfish, sesame, peanuts and oilseeds tend to last longer.

Breastfeeding is recommended for up to 6 months. It is not necessary for the mother to avoid certain allergenic foods in her diet, even in the case of a family situation. Likewise during pregnancy, no particular diet has proven its effectiveness in preventing food allergy in babies.

Previously, it was recommended to delay the introduction of certain allergenic foods in order to prevent food allergies in infants. Today, the trend is rather the opposite following studies confirming the interest of early introduction of potentially allergenic foods. It is therefore recommended to start diversification between 4 and 6 months, including for allergenic foods. Except in infants at risk (significant eczema, already existing food allergy, two poly-allergic parents), for whom it is advisable to do an allergological assessment (skin prick-tests or specific IgE dosage) before starting the diversification. Depending on the results, the diversification strategy will be adapted.