Acute viral skin and nerve infection. Groups of small blisters appear along certain nerve segments, most often on the back, sometimes after a dull ache at the site; pain becomes more severe when the blisters break out. Caused by the same virus as chickenpox, it probably results from reactivation of seemingly inactive virus in a partially immune person. Spontaneous recovery from the infection usually occurs within two weeks, but neuralgia may last months or even years longer.
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Infection caused by herpes simplex virus. Type I typically produces a cluster of small blisters (cold sores, or fever blisters), usually on the lips or face; it can also infect the eyes. Type II, transmitted mostly through sexual contact, causes genital blisters, which rupture, becoming very painful. Oral sex can give either type the chance to infect the usual site of the other. In both types, the virus remains after symptoms end and can reactivate, causing blisters to reappear. Babies born to mothers with active herpes can become infected during birth; this can be prevented by cesarean section. There is no cure, but drugs can reduce severity and risk of transmission.
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