What causes herpes on the lips?

Herpes simplex virus (HSV) can be divided into type I and type II. The first infection of HSV occurs in children under five years old. After kissing or other close contact with life, it mainly causes skin and brain infections other than genitals, especially around the mouth and nose. After the virus invades the skin mucous membrane, it can proliferate locally first, form the initial infection, and lurk in the local ganglion. When it receives some inducement, such as fever, cold, exposure, fatigue, mechanical stimulation, etc., the virus in latent state can be activated to further form the recurrence of herpes.