A high level of immunoglobulin E in children is mostly suggested to be caused by allergic factors, such as milk protein allergy and eczema. Immunoglobulin E is an immunoglobulin secreted by eosinophils, mast cells and plasma cells in human blood under the action of a series of cytokines after receiving antigenic stimulation. Human allergy is divided into rapid-onset allergic reactions, such as penicillin test sensitization, which is because the body has already produced immunoglobulin E after the first exposure to penicillin, and after re-exposure to penicillin, immunoglobulin E quickly binds with it and produces rash, vomiting, abdominal pain and even shock. There is another kind of allergic reaction in human body called delayed allergic reaction, which is mediated by T lymphocytes, and this also involves immunoglobulin E. For example, eczema, contact dermatitis, and the most common one is the card scar after BCG vaccination.