Cow’s Milk Allergy in Breastfed Infants: What Clinicians and Families Need to Know

Cow’s milk allergy (CMA) remained one of the most frequently reported food allergies in infants, with prevalence estimates ranging from less than 1% to 7.5% in those younger than 1 year.¹ Although exclusive breastfeeding has long been promoted as the gold standard for infant nutrition and immune protection, it doesn’t fully shield infants from developing CMA, which affects 0.5% to 1% of breastfed babies.² This was because cow’s milk proteins consumed by the mother could pass into breast milk and trigger symptoms in sensitive infants.

Although exclusive breastfeeding has long been promoted as the gold standard for infant nutrition and immune protection, it doesn’t fully shield infants from developing CMA, which affects 0.5% to 1% of breastfed babies. | Image credit: Irina Schmidt - stock.adobe.com

However, a new review provided a comprehensive summary of the immunological mechanisms, clinical presentations, and management challenges of CMA in exclusively breastfed infants.³

“Given the infant gut microbiome’s crucial role in allergy development, examining how the maternal diet and breast milk composition influence this ecosystem is essential for developing preventive strategies. Embracing precision nutrition, future studies should utilize genetic, immunological, and microbiome profiling to provide tailored dietary advice that meets each infant’s needs while minimizing unnecessary restrictions,” the authors wrote.

A Complicated Clinical Picture

CMA manifests through immune responses to cow’s milk proteins—most notably casein, α-lactalbumin, and β-lactoglobulin (β-LG). Infants could experience:

• IgE-mediated CMA, marked by rapid-onset symptoms such as hives or vomiting
• Non–IgE-mediated CMA, which typically causes delayed gastrointestinal symptoms or chronic conditions like food protein-induced proctocolitis
• Mixed-type CMA, which includes overlapping features

In breastfed infants, non–IgE-mediated CMA is more common but harder to diagnose, as standard allergy tests such as serum IgE or skin prick testing are often ineffective. Diagnosis often relies on maternal dietary elimination trials and observed symptom patterns, which could be subjective and lead to misinterpretation.

The review highlighted that β-LG—a major cow’s milk protein—has been detected in breast milk as early as 4 hours and as long as 7 days after maternal dairy intake. Levels varied, with some measurements reaching up to 800 μg/L. In infants with atopic dermatitis, β-LG presence in breast milk was often correlated with detection in the infant’s bloodstream, suggesting systemic exposure and symptom linkage.

This prolonged and variable presence of milk protein in breast milk made it difficult to assess whether symptoms were tied to maternal diet, especially during short elimination trials. As a result, families and clinicians sometimes continued or intensified elimination diets without clear evidence of benefit.

Overdiagnosis Risks and Future Research

The review raised concern over the potential for overdiagnosis of CMA, particularly when common infant symptoms—like occasional blood-streaked stools or mild eczema—were attributed to milk allergy without sufficient diagnostic evidence. Overdiagnosis often led to early weaning, unnecessary use of expensive hypoallergenic formulas, and excessive health care utilization.

For mothers maintaining milk-free diets, the nutritional burden was significant. Deficiencies in vitamin B12, iodine, docosahexaenoic acid, and other nutrients were common without careful supplementation. The review called for routine nutritional counseling to accompany elimination diets, particularly when they extended beyond a few weeks.

Emerging data pointed to the infant gut microbiome as a factor in both allergy development and the eventual outgrowth of CMA. Infants with CMA tended to show lower microbiome diversity and reduced levels of butyrate, a beneficial short-chain fatty acid. While most children outgrew CMA by 12 months of age, the absence of reliable biomarkers—especially in cases that did not involve IgE—means that families often face prolonged elimination diets and uncertainty around when to safely reintroduce milk.

The authors recommended that future research should focus on developing accurate, noninvasive diagnostic tools—especially for non–IgE-mediated cases. This includes validating reliable biomarkers and standardizing diagnostic criteria through high-quality clinical trials. Studies should explore how allergens transfer through breast milk and whether full elimination or threshold-level exposure better promotes tolerance. Research is also needed on the effectiveness of shorter vs prolonged elimination diets.

Long-term impacts of maternal dietary restrictions—on nutrition, bone health, and microbiota—should be examined, along with safe dairy alternatives. Precision nutrition approaches and better caregiver education tools are essential to support individualized care while avoiding unnecessary dietary burdens.

References

1. Rajani PS, Martin H, Groetch M, Järvinen KM. Presentation and management of food allergy in breastfed infants and risks of maternal elimination diets. J Allergy Clin Immunol Pract. 2020;8(1):52-67. doi:10.1016/j.jaip.2019.11.007

2. Sambrook J. Incidence of cow’s milk protein allergy. Br J Gen Pract. 2016;66(651):512. doi:10.3399/bjgp16X687277

3. Cow’s milk allergy in breastfed infants: what we need to know about mechanisms, management, and maternal role. Nutrients. 2025;17(11):1787. doi:10.3390/nu17111787