What Causes Herpes to Flare Up?

Of the 25 or so known herpes strains, eight can infect human beings, according to the Merck Manuals. The most common of the diseases caused by a herpes infection in humans include chickenpox, genital herpes and oral herpes. In each of these three diseases, the virus retreats to the nervous system and enters a state of hibernation, or latency. Under certain conditions, the virus can reactivate and cause a flare-up or recurrence.

Chickenpox to Shingles

Chickenpox is a highly contagious disease caused by the varicella zoster virus. It spreads through contact with fluid from a chickenpox blister, or through breathing airborne viral particles. Once a person has had chickenpox, it is rare that a second outbreak will ever occur. The virus can reactivate, however, and travel from the nervous system to the skin, causing an infection called shingles. Unlike chickenpox, which causes a widespread body rash, the blister-filled rash in a shingles outbreak usually erupts in a band, called a dermatome, on one side of the body. The University of Maryland Medical Center, or UMMD, reports that the band of blisters occurs most often on the trunk, neck or face. Novartis Pharmaceuticals Corp. reports that two out of every 10 people who have had chickenpox will have shingles at some time during their lifetime. Age appears to be a factor in who will experience shingles. The disease is most common in people over the age of 50. Novartis reports that a decrease in a person's immunity to the virus results through aging. Stress, major depression, immunosuppressant drugs and certain diseases may also play a role.

Oral Herpes Flares

In most cases, oral herpes is caused by the Herpes Simplex Virus, Type 1, HSV-1. UMMC reports that many people are infected in childhood, with 30 to 90 percent of people infected by the time they reach adulthood. Like the herpes strain that causes chickenpox and shingles, HSV-1 retreats to the nervous system after a person is first infected. It can reactivate any number of times over a person's lifetime, though the number of outbreaks and the severity of the outbreaks tend to lessen over time. Medline Plus reports that triggers that can cause a flare include fever, stress and exposure to excessive sunlight.

Genital Herpes

Herpes Simplex Virus, Type 2 , HSV-2, most often causes genital herpes and is usually, but not always, sexually transmitted, according to UMMC. It affects the genital area, including the buttocks, upper thighs and anal areas. It can be spread through bodily fluids, including genital and oral secretions. After the initial infection, the virus usually retreats to the sacral ganglia, a nerve center located at the base of the spine, according to the University of South Carolina. Medline Plus reports that outbreaks can be so frequent that they appear as one prolonged outbreak, or as infrequent as once a year. Many people do not even know they are infected, either because they never show symptoms, or because symptoms are so mild they misdiagnose them. Factors that affect recurrence, or flare-up, rate include the immune system's ability to control the virus. Triggers include fatigue, menstruation, localized trauma and illness.