Blisters around the mouth are usually caused by herpes simplex virus infection. The oral mucosa first becomes extensively congested and edematous, followed by clusters of small, pinhead-sized blisters on the palate, gums, and corners of the mouth. The fluid exuded from the blisters easily extends to the skin around the mouth, which expands the scope of the blisters and forms hyperpigmentation after healing, and the recurrence of blisters is caused by frequent application of chemicals such as lipstick or bright light.