In general, yellow crusts on the skin at the corners of the mouth may be impetigo, stomatitis, herpes simplex and so on. 1. Impetigo: this disease is often caused by Staphylococcus aureus, type B hemolytic streptococcus and other infections of the epidermis caused by suppurative skin disease, prevalent in infants and children. 2. Keratitis: the cause of this disease is not yet clear, may be related to malnutrition, vitamin deficiency, trauma, allergies or microbial infections, etc., which can cause flushing of the skin around the mouth, flaking, blisters, cracking, etc., and may lead to yellow crusts at the corners of the mouth. 3. Herpes simplex: contact with herpes simplex patients with intimate articles or kissing, etc. easily caused by the disease, or herpes simplex cure, due to excessive fatigue, cold, low immunity and other reasons to stimulate the potential herpes simplex virus caused by re-infection. The main manifestation is a limited cluster of small blisters, preferably at the junction of the skin and mucous membranes, which may lead to yellow scabs at the corners of the mouth. There may be other causes of yellow scabs on the skin at the corners of the mouth, and it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or therapy.