Herpes simplex (Ancient Greek: ἕρπης - herpes, lit. "creeping") is a viral disease caused by both herpes simplex virus 1 (HSV-1) and herpes simplex virus 2 (HSV-2). Infection with the herpes virus is categorized into one of several distinct disorders based on the site of infection. Oral herpes, the visible symptoms of which are colloquially called cold sores or fever blisters, infects the face and mouth. Oral herpes is the most common form of infection. Genital herpes, known simply as herpes, is the second most common form of herpes. Other disorders such as herpetic whitlow, herpes gladiatorum, ocular herpes (keratitis), cerebral herpes infection encephalitis, Mollaret's meningitis, neonatal herpes, and possibly Bell's palsy are all caused by herpes simplex viruses. Herpes viruses cycle between periods of active disease—presenting as blisters containing infectious virus particles—that last 2–21 days, followed by a remission period, during which the sores disappear. Genital herpes, however, is often asymptomatic, though viral shedding may still occur. After initial infection, the viruses move to sensory nerves, where they reside as life-long, latent viruses. Causes of recurrence are uncertain, though some potential triggers have been identified. Over time, episodes of active disease reduce in frequency and severity. Herpes simplex is most easily transmitted by direct contact with a lesion or the body fluid of an infected individual. Transmission may also occur through skin-to-skin contact during periods of asymptomatic shedding. Barrier protection methods are the most reliable method of preventing transmission of herpes, but they merely reduce rather than eliminate risk. Oral herpes is easily diagnosed if the patient presents with visible sores or ulcers. Early stages of orofacial herpes and genital herpes are harder to diagnose; laboratory testing is usually required. Twenty percent of the U.S. population has antibodies to HSV-2, although not all of them have a history of genital lesions. A cure for herpes has not yet been developed. Once infected, the virus remains in the body for life. However, after several years, some people will become perpetually asymptomatic and will no longer experience outbreaks, though they may still be contagious to others. Vaccines are in clinical trials but have not demonstrated effectiveness. Treatments can reduce viral reproduction and shedding, prevent the virus from entering the skin, and alleviate the severity of symptomatic episodes. Herpes simplex should not be confused with conditions caused by other viruses in the herpesviridae family such as herpes zoster, which is a viral disease caused by varicella zoster virus. There is also a possibility of confusion with hand, foot and mouth disease due to apparition of lesions on the skin.