In most people, the virus can become active several times a year. This is called a recurrence. But scientists do not yet know why this happens. When it becomes active again, it travels along the nerves to the skin, where it busies itself by making more viruses near the site of the very first infection. That is where new sores usually will appear.
Sometimes, the virus can become active but not cause any sores that can be seen. At these times, small amounts of the virus may be shed at or near places of the first infection, in fluids from the mouth, penis, or vagina, or from barely noticeable sores. You may not notice this shedding because it often does not cause any pain or feel uncomfortable. Even though you might not be aware of the shedding, you still can infect a sex partner during this time.
After the first outbreak, any future outbreaks are usually mild and last only about a week. An infected person may know that an outbreak is about to happen by feeling a tingling feeling or itching in the genital area, or pain in the buttocks or down the leg. For some people, these early symptoms can be the most painful and annoying part of an episode. Sometimes, only the tingling and itching are present and no visible sores develop. At other times, blisters appear that may be very small and barely noticeable, or they may break into open sores that crust over and then disappear.
The frequency and severity of the recurrent episodes vary greatly. While some people have only one or two outbreaks in a lifetime, others may have several outbreaks a year. The number and pattern of repeat outbreaks often change over time for a person. Scientists do not know what causes the virus to become active again. Although some people with herpes report that their outbreaks are brought on by another illness, stress, or having a menstrual period, outbreaks often are not predictable. In some cases, outbreaks may be connected to exposure to sunlight.
Reprinted from the National Institute of Allergy and Infectious Diseases, National Institutes of Health

