Erythromycin ointment can usually be applied if the blisters on the mouth are the result of a condition such as acne vulgaris or impetigo. Erythromycin ointment should not be applied if it is the result of an allergy or viral infection. Erythromycin ointment is a macrolide antibiotic. Determining whether or not erythromycin ointment can be applied to blisters on the mouth depends on the specific case, and cannot be generalized, but depends mainly on the cause of the disease. If the blisters are caused by acne vulgaris, impetigo, or a small burn, erythromycin ointment can usually be applied as prescribed. However, if the blisters on the mouth are caused by an immune response due to allergies, as well as herpes simplex virus infections, then erythromycin ointment should not be applied and will not have any therapeutic effect. Secondly, patients should not apply erythromycin ointment to the mouth and nasal cavity when using it externally. To summarize, there are many causes of blisters on the mouth, patients need to go to the hospital, under the guidance of the doctor’s medication, do not use erythromycin ointment on their own, so as not to delay the condition.