If you think your baby may be allergic to the protein in cow’s milk, keep an eye out for symptoms such as body rash, coughing, wheezing, vomiting, and diarrhea. Delayed reactions can present slightly differently, with spit-up, constipation, eczema, and extreme fussiness. There are blood and skin prick tests that can properly diagnose this allergy, so consult your pediatrician for answers and next steps.