Blisters on the mouth may be recurrent herpes labialis due to herpes simplex virus infection, as described below. Herpes simplex virus infection can cause primary herpetic gingivostomatitis, and recurrent damage may occur in some patients after the primary herpes infection has healed, usually occurring on or near the lips and called recurrent herpes labialis. Irritation, burning, and itching may be felt in and around the lips before blistering, followed by the appearance of multiple clusters of blisters, which may undergo rupture, erosion, and crusting. If secondary infection occurs, small pustules may also appear on the lesions. There may be other causes of blisters on the mouth, it is recommended to go to the hospital in time to clarify the cause of the disease for targeted treatment.