People with mouth sores at the corners of the mouth may have a herpes virus infection that causes herpetic keratitis, which should be treated by applying antiviral medication, such as acyclovir ointment, to the localized blistered area at the corners of the mouth. If the area of the sore at the corner of the mouth is red, swollen and vesicular, this indicates that a bacterial infection has developed and can be treated by applying erythromycin ointment locally for anti-inflammatory treatment. Mouth sores at the corners of the mouth may also be caused by chronic lip infection, which causes dryness, flaking and erosion of the lips, mostly due to vitamin and micronutrient deficiencies in the body, so vitamin B2 ointment, vitamin B6 ointment and vitamin B12 ointment can be applied to the mouth sores at the corners of the mouth. If the lip sores at the corners of the mouth do not heal for a long time and the symptoms are very serious, you need to go to the hospital and apply ointments containing hormones for treatment under the guidance of a doctor.