Paralysis of all muscles of facial expression (corner of mouth droops, palpebral fissure is widened, forehead is unfurrowed) which has a sudden onset. It is due to lesion of the VIIth nerve, and may be accompanied by loss of taste sensation, and reduced salivation and lacrimation depending on exactly which components are involved. Causation is unclear. About 90% of patients have only demyelination of the nerve, and recover in a few weeks; a longer recovery period is required if axon degeneration has occurred. Axon regeneration may take over a year, and is often incomplete.