Herpes in the mouth is typically a result of a herpes simplex 1 infection. Herpes simplex 1 usually produces oral herpes, though it can also, rarely, cause a genital herpes infection. A herpes simplex 1 infection does not always present symptoms, but when it does symptoms are typically a blister outbreak about the area of the mouth, including inside of the mouth. The blisters a herpes simplex 1 infection causes are commonly referred to as cold sores. During an active outbreak of symptoms, herpes simplex is most contagious. When herpes symptoms are present, prevent others from coming into contact with symptoms to avoid spreading. It is possible to spread a herpes in the mouth infection to another person's genitals through oral sex. This is not common, but it does happen. It's also possible to get a herpes in the mouth infection through performing oral sex on another person. This is also a rare occurrence, but again, it does happen. Herpes in the mouth is not a serious threat to overall health.