Trauma to the nail causes peeling nails, according to Healthline. The source of the trauma to the nail may be from internal or external factors.
Some external sources of trauma to the nail include overuse of the nail as a tool or prolonged exposure to water or chemicals. If it is unclear whether the cause is internal or external, then a comparison between the fingernails and toenails is often helpful, says Healthline. If the peeling is present in both fingernails and toenails, then the cause is most likely to be internal. Internal causes of peeling nails include a vitamin deficiency, usually iron, or a pathological process occurring in the body.