Hidden Food Allergy Sends Children to Emergency Rooms as Canadian Study Reveals Warning Signs

A little-known food allergy can cause infants and young children to develop severe vomiting, lethargy and dehydration several hours after eating, without the hives, facial swelling or breathing difficulties commonly associated with an allergic reaction.

A new Montreal study is helping doctors and parents recognize the warning signs of Food Protein-Induced Enterocolitis Syndrome, known as FPIES, a delayed immune reaction that causes inflammation in the intestines and can send children to emergency departments.

Researchers at the Research Institute of the McGill University Health Centre followed 87 children with physician-diagnosed FPIES. The participants ranged in age from one month to 13 years and received care at the Montreal Children’s Hospital and affiliated clinics between November 2021 and April 2025.

Published in the International Archives of Allergy and Immunology, the research is the first Canadian cohort study dedicated to FPIES, according to the McGill University Health Centre.

Dr. Moshe Ben-Shoshan, the study’s lead author and a pediatric allergist and immunologist at the Montreal Children’s Hospital, said FPIES can lead to intense vomiting, severe fatigue and dehydration within a few hours of eating certain foods.

Because the reaction does not usually produce the more familiar signs of food allergy, the condition may be mistaken for a stomach virus, food poisoning or another gastrointestinal illness.

Unlike conventional IgE-mediated food allergies, FPIES generally does not cause hives, itching, redness, facial swelling or respiratory symptoms. Its delayed presentation can make the connection between the illness and a particular food difficult to identify.

The study found that symptoms began between one and four hours after eating the triggering food in 71.7 per cent of cases.

Vomiting was by far the most frequently reported symptom, appearing in 93.8 per cent of recorded reactions. Repeated vomiting occurred in 71.3 per cent of cases.

Other reported symptoms included lethargy in 27.8 per cent of reactions, pallor in 23.7 per cent, diarrhea in 15.5 per cent, abdominal pain in 10.3 per cent and dehydration in 9.3 per cent. Low blood pressure and low body temperature were reported only rarely.

Researchers classified 18 per cent of the reactions as severe.

Parents should pay particular attention when a child begins vomiting repeatedly one to four hours after eating a specific food, especially when the reaction is accompanied by unusual sleepiness, weakness, pale or grey-looking skin, diarrhea or signs of dehydration.

Warning signs of dehydration may include a dry mouth, reduced urination, crying without tears, unusual drowsiness or difficulty drinking enough fluids.

Food Allergy Canada warns that serious FPIES reactions may include severe vomiting, diarrhea, dehydration, grey or blue-looking skin and, in rare cases, shock. Emergency services should be contacted when a child develops serious symptoms or appears severely unwell.

According to the Montreal study, 36.8 per cent of the children were brought to a health-care facility for treatment, while 63.2 per cent were managed at home.

Oral hydration was the most common treatment provided outside a medical facility. Some children treated in health-care settings received oral fluids, the anti-nausea medication ondansetron or intravenous fluids. The study also noted that antihistamines have limited usefulness in FPIES because the condition is not primarily mediated by IgE antibodies.

The median age at the time of a reaction was seven months, and most reactions occurred before the age of two. This is also the period when families commonly begin introducing formula, solid foods and new ingredients into an infant’s diet.

Egg was the most common trigger identified in the study, accounting for 27.6 per cent of recorded reactions. Shellfish represented 21 per cent, followed by milk at 11.2 per cent.

Fish and peanuts each accounted for 10.3 per cent, while other triggers included oats, fruit, soy, grains and rice.

Approximately 41 per cent of reactions occurred after a child’s first known exposure to the triggering food, and nine per cent of the children reacted to two or more foods.

Researchers also found that 41.9 per cent of the children had eczema or atopic dermatitis, 20.4 per cent had another food allergy and 14 per cent had asthma. However, 36.6 per cent had none of those accompanying conditions.

Traditional allergy testing may not provide a clear answer. Skin-prick tests were performed on 75.3 per cent of participants, and 90 per cent tested negative for the food responsible for their FPIES reaction.

Diagnosis therefore depends heavily on a detailed medical history, the timing of symptoms and whether the same pattern occurs after a particular food is eaten.

Families should not remove several foods from a child’s diet or reintroduce a suspected trigger after a serious reaction without guidance from a pediatric allergist or another qualified health-care professional.

When doctors need to determine whether a child has outgrown the condition, they may recommend a medically supervised oral food challenge. This allows the food to be reintroduced in a controlled setting where treatment is available if another reaction occurs.

The findings also offered reassurance to families. Among children who attempted to eat their triggering food again during follow-up, 81 per cent no longer developed symptoms.

The study reported that resolution occurred most often during the first year after diagnosis, particularly in children whose reactions were triggered by egg or milk. Many young children with FPIES eventually develop tolerance as they grow older.

Researchers said greater awareness among parents, family doctors, pediatricians and emergency physicians could help reduce delayed diagnoses, repeated hospital visits and unnecessary treatments.

The research team plans to expand its work to other Canadian provinces to examine whether triggers, treatment practices and recovery patterns differ across the country.