A rupture at the corner of the mouth is most likely caused by a herpes simplex virus infection. Herpes simplex virus exists in the posterior ganglion of the ear in adults, and when the resistance is low, inflammation will appear in the corner of the mouth, and you can apply acyclovir ointment, which has a very good antiviral effect. And active nutritional support, early rest, avoid excessive mental stress, until the resistance to improve the corners of the mouth herpes will naturally improve, generally this viral infection has a period of cure, the course of the disease about 7-15 days, 15 days after the natural will be completely cured. However, the virus will not be completely eliminated, but will return to the ganglion behind the ear, and when the resistance is not enough, the corners of the mouth may become inflamed again.