Abstract
Cow's milk protein allergy (CMPA) is one of the urgent problems of modern health care, which pediatricians often encounter in their practice. CMPA imposes a burden on babies and their mothers, forcing them to limit their diet and plan the family budget, taking into account the cost of therapeutic infant formulas. Also, CMPA is still a challenging diagnosis since it can present in three variants and has various developing mechanisms. The elimination diet is the most reliable test in an infant with suspected CMPA. All dietary restrictions are imposed on the mother if the baby receives breast milk. The article presents a clinical case of CMPA in a breastfed infant, which occurred when a formula was included in the diet and presented with rashes, mucus diarrhea, constipation, and projectile vomiting.