A cold sore on this patient’s lip was caused by the herpes simplex virus type 1 (HSV-1).
Herpes, a very common viral infection, spreads by person-to-person contact.
The infection is caused by the herpes simplex virus (HSV), which comes in two forms: HSV-1, which usually results in oral herpes infections affecting the mouth and lips; and HSV-2, which usually causes genital herpes affecting the genitals and anus.
Both types of HSV spread primarily by physical contact with an infected person. Most people get HSV-2 during sexual intercourse (vaginal or anal). HSV-1 tends to spread to individuals in childhood, when an adult who carries the virus touches the child — for example, by pinching a baby's cheeks. Among adults, HSV-1 usually spreads by kissing.
However, HSV-1 can also spread to the genitals during oral sex, while HSV-2 infections in the genitals can spread to the mouth during oral sex.
About 50 to 80 percent of U.S. adults carry HSV-1 (oral herpes), while 20 percent of people age 12 and older have HSV-2. In many cases, however, individuals with the virus don't know they have it. In fact, an estimated 90 percent of people with HSV-2 don't know they're infected.
That's because many people carry herpes without showing any signs of it. One symptom of a herpes infection is the presence of sores around the mouth, genitals or anus. These sores appear during a so-called herpes "outbreak" but usually clear up on their own.
The virus, however, never goes away — once you've been infected with herpes, it sticks with you forever. Most of that time, it will be dormant, living in your nerve cells (instead of in the skin cells, where it can cause sores).
People with dormant herpes virus can still pass it to others, though outbreaks of herpes sores make transmission more likely. Using barriers like condoms and dental dams during sex can lower your risk of getting herpes, but they are not 100 percent effective.