Fever blisters are small sores in the mouth or the area around it. They usually develop on the gums, roof of the mouth, outside of the lips, or the nostrils.
Fever blisters are caused by the two types of herpes simplex virus. Most fever blisters are caused by herpes simplex virus 1, or HSV 1, which causes oral herpes. The virus that causes genital herpes, HSV 2, may also cause fever blisters.
The two stages of oral herpes are primary infection and recurrence of infection. At some time during childhood, most people come down with the primary infection. The individual may or may not have symptoms. This primary infection takes about 2 weeks to clear up. After that, the virus remains in the body but is inactive.
After this primary infection, there can be a recurrence at any time. Many outbreaks occur without any obvious reason. However, the following factors may trigger a recurrence:
Fever blisters are caused by a herpes virus. People in the following categories may be more at risk for oral herpes: