Disease the time between infection and the appearance of symptoms. The latency period is the time between infection and the ability of the disease to spread to another person, which may precede, follow, or be simultaneous with the appearance of symptoms. Some viruses also exhibit a dormant phase, called viral latency, in which the virus hides in the body in an inactive state. For example, varicella zoster virus causes chickenpox in the acute phase; after recovery from chickenpox, the virus may remain dormant in nerve cells for many years, and later cause herpes zoster (shingles). Diseases may be classified by cause,
Psychogenic disease to be psychogenic include psychogenic seizures, psychogenic polydipsia, psychogenic tremor, and psychogenic pain. There are problems with the assumption that all medically unexplained illness must have a psychological cause. It always remains possible that genetic, biochemical, electrophysiological, or other abnormalities may be present which we do not have the technology or background to identify. The term "psychogenic disease" is often used in a similar way to "psychosomatic disease". However, the term "psychogenic" usually implies that psychological factors played a key causal role in the development of the illness. The term "psychosomatic" is often used in a broader way to describe