Oral herpes is usually caused by HSV-1. The highest incidence of first infection occurs between 6 months and 3 years of age. The incidence in children varies among regions and countries, with the highest rates occurring in crowded and unsanitary regions. Studies suggest that by age 5 more than a third of children in low-income areas are infected compared to 20% of children in middle-income areas. However, by the time Americans of all economic backgrounds reach age 60, about 60 - 85% have become infected with HSV-1.

To infect people, the herpes simplex viruses (both HSV-1 and HSV-2) must get into the body through broken skin or a mucous membrane, such as inside the mouth or on the genital area. Each virus can be carried in bodily fluids (saliva, semen, fluid in the female genital tract) or in fluid from herpes sores. The risk for infection is highest with direct contact of blisters or sores during an outbreak.

Herpes simplex transmission

Once the virus has contact with the mucous membranes or skin wounds, it begins to replicate. The virus is then transported within nerve cells to their roots where it remains inactive (latent) for some period of time. During inactive periods, the virus cannot be transmitted to another person. However, at some point, it often begins to multiply again without causing symptoms (called asymptomaticshedding). During shedding, the virus can infect other people through exchange of bodily fluids.

Sometimes, infected people can transmit the virus and infect other parts of their own bodies (most often the hands, thighs, or buttocks). This process, known as autoinoculation, is uncommon, since people generally develop antibodies that protect against this problem.

Transmission of Oral Herpes. Oral herpes is usually caused by HSV-1. HSV-1 is the most prevalent form of herpes simplex virus, and infection is most likely to occur during preschool years. Oral herpes is easily spread by direct exposure to saliva or even from droplets in breath. Skin contact with infected areas is enough to spread it. Transmission most often occurs through close personal contact, such as kissing. In addition, because herpes simplex virus 1 can be passed in saliva, people should also avoid sharing toothbrushes or eating utensils with an infected person.