Cow’s milk protein allergy (CMPA) is one of the most common food allergies in infants, presenting with either IgE-mediated or non-IgE-mediated immunological mechanisms. The transition from non-IgE- to IgE-mediated allergy can lead to severe reactions, including anaphylaxis. A 40-day-old exclusively breastfed infant presented with bloody and mucous stools due to non-IgE-mediated allergic proctocolitis. After 48 h of milk elimination from the mother’s diet, the symptoms resolved. However, at 7.5 months, after consuming yogurt, the infant developed anaphylaxis with generalized urticaria and vomiting. An IgE-mediated anaphylaxis diagnosis was confirmed. Adrenaline was administered, and close follow-up was established. Food allergies, especially those related to cow’s milk proteins, can evolve from a non-IgE- to an IgE-mediated form, presenting with more severe symptoms, including anaphylaxis. Diagnosis relies on clinical evaluation, skin tests, and specific IgE measurements. This evolution highlights the importance of long-term monitoring for infants at risk. Cow’s milk protein allergy can evolve and worsen over time. Immunological changes must be closely monitored, especially during the gradual introduction of dairy products after an elimination period. Rigorous follow-up and education of parents about anaphylaxis are critical.