The appearance of extra-oral herpes may be related to viral infection, allergic herpes and other factors. 1. Viral infection: Extra-oral herpes is most likely caused by herpes simplex due to herpes virus infection. After being infected by herpes virus, it will lurk in the nerve roots for a long time, and most often appears during periods of immune deficiency such as colds, fever and fatigue. It usually appears as a cluster of blisters, and when the blisters rupture, white mucus will flow out, accompanied by localized swelling and pain. 2. Allergic herpes: allergies to cosmetics or food can also cause extra-oral herpes, which is often accompanied by localized itching, and need to exclude allergens in time to avoid repeated allergies. It is recommended to go to the dermatology department for a clear diagnosis and treatment after the appearance of extra-oral herpes, so as not to delay the condition.