How to detect Cow milk Allergies in Babies - One of common case in babies are Not all of them can be given formula derived from cow's milk. If your baby has an allergy, the vary reaction can happen. A reaction from mild to severe can appear within minutes or hours after he consumed cow's milk or foods which are contaminated by it, including the breast milk of mothers who drink cow's milk. This condition is called an allergy to cow's milk.