Food allergies occur when an infant’s immune system mistakenly identifies a harmless food protein as a threat. This immune response triggers reactions that can affect the skin, respiratory tract, and gastrointestinal tract. Vomiting is a common manifestation of a food allergy, but it must be distinguished from the frequent, non-forceful spitting up typical of a healthy infant. Understanding the nature and timing of the vomiting is the first step in determining if the reaction is allergic.
Vomiting as a Symptom of Food Allergy
Vomiting caused by a food allergy manifests in two different ways, depending on the immune system response. The first type is an immediate, or Immunoglobulin E (IgE)-mediated, reaction. The body releases chemicals like histamine within minutes of ingesting the food, causing the gut muscles to contract violently. This results in sudden, often singular episodes of vomiting shortly after a feeding, as part of a rapid, systemic reaction.
The second type is a delayed, non-IgE-mediated reaction, such as Food Protein-Induced Enterocolitis Syndrome (FPIES). In FPIES, the vomiting is repetitive, profuse, and projectile, beginning one to four hours after the trigger food is eaten. This severe reaction is caused by inflammation in the intestines, leading to a fluid shift into the gut.
FPIES can be severe, leading to dehydration, paleness, and lethargy in the infant. Common triggers include cow’s milk, soy, and grains like rice or oat. Since this reaction is delayed and non-IgE mediated, standard allergy tests like skin prick tests will not detect it.
Recognizing Other Associated Symptoms
Vomiting is rarely the only sign of a true food allergy, and the presence of other symptoms helps confirm the underlying cause. Immediate IgE-mediated allergies often involve multiple organ systems simultaneously. Skin symptoms may include the rapid onset of hives (raised, red welts) or angioedema (swelling of the lips, eyes, or face).
Respiratory symptoms often accompany immediate reactions, such as wheezing, a persistent cough, or nasal congestion. These reactions are rapid, appearing within minutes to two hours of exposure. The combination of symptoms across different systems indicates an IgE-mediated allergy.
In contrast, non-IgE-mediated conditions like FPIES and Food Protein-Induced Allergic Proctocolitis (FPIAP) primarily affect the gastrointestinal tract. While FPIES causes severe, delayed vomiting, FPIAP is characterized by blood or mucus in the stool, often without vomiting. Other gastrointestinal symptoms that may accompany non-IgE vomiting include chronic diarrhea, abdominal discomfort, and poor weight gain due to malabsorption.
Ruling Out Other Causes of Infant Vomiting
Differentiating allergic vomiting from common, non-allergic causes is essential. Normal infant spitting up, or gastroesophageal reflux (GER), is a passive overflow of stomach contents without forceful muscle contractions. Spitting up is painless, occurs shortly after feeding, and the infant remains healthy and gains weight appropriately.
Forceful vomiting involving abdominal muscle contraction can be caused by viral gastroenteritis (a stomach bug). Viral vomiting is usually accompanied by a fever, and symptoms, including diarrhea, resolve within a few days. Allergic vomiting, especially FPIES, lacks fever and recurs every time a specific food protein is consumed.
Anatomical issues, such as pyloric stenosis, also cause forceful, projectile vomiting. This differs from allergic vomiting because it is a structural problem, not an immune reaction, and the vomiting is constant and progressive regardless of food type. In contrast, symptoms of chronic non-IgE allergies, including vomiting, clear up completely when the specific trigger food is removed from the diet.
Next Steps for Diagnosis and Management
If an infant experiences repetitive, forceful vomiting accompanied by extreme paleness or lethargy, immediate medical attention is necessary. This may indicate severe dehydration or a severe FPIES reaction. For immediate IgE-mediated symptoms, such as hives or swelling combined with vomiting, emergency medical services should be contacted, as this can signal anaphylaxis.
For less severe, chronic symptoms like intermittent vomiting, diarrhea, or blood in the stool, a routine visit with a pediatrician is appropriate. Diagnosis begins with a detailed clinical history, documenting the timing of symptoms relative to specific feedings. For suspected IgE allergies, a specialist may perform skin prick tests or blood tests to measure IgE antibodies.
Non-IgE conditions like FPIES cannot be diagnosed with standard tests. Diagnosis relies on symptom resolution after an elimination diet, followed by a medically supervised oral food challenge to confirm the trigger food. Management involves strictly avoiding the identified food and, for FPIES, having a plan for acute reactions, which may include administering intravenous fluids in a medical setting. Consulting an allergist or pediatric gastroenterologist is important for accurate diagnosis and long-term management.