Casein intolerance happens when the body sees casein as a threat instead of a healthy peptide that it is. In those cases, the immune system responds by triggering the synthesis of IgE antibody, which leads to histamine production. Key Symptoms of Casein Intolerance are : Swelling of lips, tongue, mouth, face, and throat Skin reactions namely rash, itching, redness and hives Nasal congestion, sneezing, running nose, watery and itchy eyes, coughing, wheezing and shortness of breath GI disturbances like flatulence, bloating, abdominal cramping and frothy diarrhea. Anaphylaxis Anaphylaxis is a potentially fatal reaction that occurs rapidly and needs immediate medical attention.