The cause of itchy skin and scratch a red, consider and external stimulation, artificial urticaria, angioedema and so on. 1. external stimulation: some patients may be dry skin and thus itchy, in the case of scratching, the skin will produce a stress reaction, itchy skin scratching a red symptom. 2. Artificial urticaria: usually refers to the skin after scratching the symptoms of striae or redness, the specific etiology has not been clarified, may be related to mechanical stimulation of the skin, so it will make the hypertrophic cells to release vasoactive mediators, resulting in itchy skin scratching a red symptom. 3. Angioedema: also known as “giant urticaria”, mainly due to subcutaneous loose tissue, submucosal expansion of small blood vessels and osmotic pressure caused by increased, often occurring in allergic populations, so the patient will have itchy skin scratch a red phenomenon. Simply based on the itchy skin scratch a red syndrome can not accurately determine the cause, but also need to be combined with the characteristics of the medical history, other test results in order to make an accurate judgment, it is recommended that the cause of the disease under the guidance of the doctor to clarify the cause of the disease, and comply with the doctor’s instructions for treatment.