There are many reasons for the sudden redness and itching of the face, such as physiological factors (e.g. environmental stimuli, change of season, etc.) or pathological factors (e.g. allergic diseases, infectious diseases, etc.). 1. Physiological factors: (1) Environmental stimulation: prolonged exposure to the sun, cold wind stimulation, etc., may lead to skin irritation, resulting in sudden redness and itching of the face. (2) Seasonal change: Sudden redness and itching of the face may also be due to the change of season, after the change of season, there is a big difference between hot and cold temperatures, which may cause skin sensitivity, skin dryness, thus causing sudden redness and itching of the face. 2. Pathologic factors: (1) Allergic diseases: eating allergic food, contact with allergic substances, etc., may lead to the phenomenon of sudden redness and itching of the face, such as contact dermatitis, eczema, urticaria, etc., will be due to allergic factors caused by the sudden redness and itching of the face. (2) infectious diseases: human immunity decline, bacterial or fungal infections in the face, can appear dengue, cellulitis and other diseases, localized erythema, there may be local lymph node enlargement, accompanied by itching or swelling and pain, which leads to the phenomenon of sudden redness and itching of the face. There are many reasons for the sudden redness and itchiness of the face, and it is recommended that patients go to the hospital in time to complete the examination and give standardized treatment after a clear diagnosis.