Importance: Sales of specialized formula for managing cow's milk allergy (CMA) have increased, triggering concern that attribution of common infant symptoms, such as crying, vomiting, and rashes, to CMA may be leading to overdiagnosis, which could undermine breastfeeding. Objective: To understand whether CMA guideline recommendations might promote CMA overdiagnosis or undermine breastfeeding. Evidence Review: We reviewed recommendations made in CMA guidelines and critically appraised 2 key recommendations. First, we reviewed relevant literature summarizing whether maternal or infant dietary exclusion of cow's milk is effective for managing common infant symptoms. Second, we reviewed published data on breastmilk composition and thresholds of reactivity in CMA to estimate the probability that cow's milk protein in human breastmilk can trigger symptoms in infants with CMA. We also documented the level of commercial involvement in CMA guidelines. Findings: We reviewed 9 CMA guidelines published from 2012 to 2019. Seven suggest considering CMA as a cause of common infant symptoms. Seven recommend strict maternal cow's milk exclusion for managing common symptoms in breastfed infants. We found CMA proven by food challenge affects approximately 1% of infants, while troublesome crying, vomiting, or rashes are each reported in 15% to 20% of infants. We found clinical trials do not provide consistent support for using maternal or infant cow's milk exclusion to manage common symptoms in infants without proven CMA. We estimated that for more than 99% infants with proven CMA, the breastmilk of a cow's milk-consuming woman contains insufficient milk allergen to trigger an allergic reaction. Three CMA guidelines were directly supported by formula manufacturers or marketing consultants, and 81% of all guideline authors reported a conflict of interest with formula manufacturers. Conclusions and Relevance: Recommendations to manage common infant symptoms as CMA are not evidence based, especially in breastfed infants who are not directly consuming cow's milk. Such recommendations may cause harm by undermining confidence in breastfeeding.