Onycholysis is the separation of a fingernail or toenail from its pink nail bed. The separation occurs gradually and is painless.
The most common cause of onycholysis is trauma. Even slight trauma can cause onycholysis when it happens repetitively — for example, the daily tapping of long fingernails on a keyboard or counter. Onycholysis also can be caused by manicure tools that are pushed beneath the nail to clear dirt or smooth the nail. Too much moisture also can cause the problem.
Some medical conditions can cause onycholysis, generally by changing the nail's shape or the contour of the soft tissue bed beneath it. In these situations, the nail cannot attach smoothly to the nail bed.
Fungal infections of the nails thicken the tissue immediately underneath the nail plate and cause edge of the nail to lift.
The skin condition psoriasis is a common cause of onycholysis.
After exposure to some medicines (notably medicines from the psoralen, tetracycline or fluoroquinolone groups) the nail can react to sun exposure by lifting away from its bed.
An overactive thyroid gland can cause onycholysis.