About 10 percent of oral herpes cases in adults are acquired by oral-genital sex with a person with active genital herpes. Most people experience their first infection with herpes simplex 1 when they are less than 10 years of age. In these primary infections, the virus usually invades the moist membrane cells of the lips, mouth, or throat. The majority of persons infected have no symptoms, but about 15 percent develop many fluid-filled blisters inside and outside the mouth three to five days after they are exposed to herpes simplex 1. The blisters may be accompanied by fever, swollen neck glands, and general aches.
Fever blisters tend to merge and then collapse.
Often a yellowish crust forms over the sores, which usually heal without scarring within 2 weeks. The herpes virus, however, stays in the body. Once a person is infected with oral herpes, the virus remains in a nerve located near the cheekbone. The virus may stay permanently inactive in this site or occasionally may travel down the nerve to the skin surface where it causes a recurrence of fever blisters. Recurring blisters generally erupt at the outside edge of the lip or the edge of the nostril, and take almost as long to heal as the initial fever blisters.