Clinical Manifestations of Dairy Allergy in Infants
Dairy allergy in infants presents through two distinct mechanisms—IgE-mediated reactions occurring within minutes to 2 hours with skin, respiratory, and gastrointestinal symptoms, or non-IgE-mediated reactions presenting with chronic gastrointestinal symptoms like bloody stools, diarrhea, and failure to thrive. 1
IgE-Mediated Reactions (Immediate: Minutes to 2 Hours)
Cutaneous Manifestations
- Hives (urticaria), flushing, and swelling of lips/tongue/face (angioedema) occur in the majority of cases 1
- Itching and redness of skin 1
- Worsening of pre-existing atopic dermatitis 1
- Critical caveat: 10-20% of anaphylactic reactions have NO skin symptoms 1
Respiratory Symptoms
- Occur in up to 70% of IgE-mediated cases 1
- Wheezing, cough, shortness of breath 1
- Nasal congestion, throat tightness, hoarseness 1
- Stridor (high-pitched breathing sound indicating airway narrowing) 1
Gastrointestinal Symptoms
- Occur in up to 40% of IgE-mediated cases 1
- Vomiting, cramping abdominal pain, and diarrhea within minutes to 2 hours 1
- Nausea 1
Cardiovascular/Systemic (Anaphylaxis)
- Weak pulse, dizziness, passing out (syncope), or hypotonia (floppiness in infants) 1
- Tachycardia (rapid heart rate) may indicate shock even without hypotension 1
- In infants, hypotension is a LATE sign—tachycardia appears first 1
- Deaths occur within 30 minutes to 2 hours, usually from cardiorespiratory compromise 1
Non-IgE-Mediated Reactions (Delayed: Hours to Days)
Food Protein-Induced Allergic Proctocolitis (FPIAP)
- Most common manifestation of dairy allergy in infants 2
- Mucoid, blood-streaked stools in an otherwise healthy, well-appearing infant 3, 2
- Can occur in both formula-fed AND exclusively breastfed infants 2, 4
- May also present with chronic vomiting and failure to thrive 3
Food Protein-Induced Enterocolitis Syndrome (FPIES)
- Chronic vomiting, diarrhea, and failure to thrive 3
- Symptoms develop hours to days after exposure 1, 5
- More severe than proctocolitis 3
Food Protein-Induced Enteropathy
- Chronic diarrhea with steatorrhea (fatty stools) in up to 80% of cases 3
- Weight loss and growth failure 3
- Generalized malabsorption of fats, carbohydrates, and nutrients 3
- May develop anemia, hypoproteinemia, and vitamin K deficiency 3
Chronic Symptoms
- Persistent eczema despite optimal topical therapy 1, 6
- Chronic ill health with symptoms developing days after milk ingestion 7
Critical Timing Patterns
IgE-mediated reactions: Symptoms begin within minutes to 2 hours after dairy ingestion 1, 5
Non-IgE-mediated reactions: Symptoms occur hours to days after exposure and are chronic in nature 1, 5, 7
Biphasic Reactions: A Critical Pitfall
- 1-20% of anaphylactic reactions recur after initial resolution 1
- Recurrence typically occurs 8 hours later but can occur up to 72 hours after the first reaction 1
- This is why observation periods are critical after initial treatment 1
Important Distinctions
Dairy allergy vs. lactose intolerance: Lactose intolerance causes bloating, flatulence, and diarrhea due to lactase enzyme deficiency WITHOUT immune involvement—it is NOT an allergic reaction 3, 6
Breastfed infants: Food proteins from maternal diet are secreted in breast milk in sufficient amounts to trigger reactions in sensitized infants, including anaphylaxis and bloody stools 2, 4
When to Suspect Dairy Allergy
- Any infant with moderate-to-severe atopic dermatitis persisting despite optimized topical therapy 1, 6
- Reproducible symptoms within minutes to hours of dairy exposure 6
- Blood-streaked stools in an otherwise healthy infant 3, 2
- Chronic diarrhea, vomiting, or failure to thrive in the first year of life 3, 8