Not medical Advice: It's a sign of herpes simplex virus (HSV).
Symptoms of HSV includes: painful vesicles develop on the lips, the gingiva, the palate, or the tongue and are often associated with erythema and edema.
The herpes simplex virus is a contagious virus that can be passed from person to person through direct contact. Children will often contract HSV-1 from early contact with an infected adult. They then carry the virus with them for the rest of their life.
Here are 10 ways to reduce the risk for genitál herpes shared by WebMD.