Onycholysis is a nail disorder characterized by separation of the nail plate from the nail bed. It frequently begins at the free edge and extends upward to the cuticle area. Less frequently, it begins at the cuticle area and extends downward. Onycholysis is most often caused by fungal and bacterial infections, excess moisture under and around the nail, and trauma. It can also result from medical conditions such as anemia, diabetes mellitus, hyper- and hypo- thyroidism, impaired oxygen and blood circulation, leprosy, lupus, sarcoidosis, syphilis, pregnancy, psoriasis, dermatitis, hyperhidrosis, congenital abnormalities of the nail, and carcinoma of the nail bed.
As a nail professional and soon to be nurse, the majority of onycholysis cases I’ve seen, resulted from trauma or fungal infections. Types of trauma includes: items being dropped on the hands, feet, or nails; stumping of the toe on hard objects; using shard tools to clean under the nails; and long toenails hitting the top of closed toe shoes (i.e. runners and walkers). Fungal and bacterial infections are often due to excess moisture, walking around barefoot, and getting pedicures at unsanitary salons.
To prevent onycholysis caused by trauma and infections, you should: dry feet thoroughly before enclosing them in socks and shoes; avoid wearing dark colored socks because fungus and bacteria breed in moist-dark conditions; keep toenails short or flushed with the skin; and use blunt implements to clean under nails using light strokes.
If you suspect that your finger or toe nails are undergoing onycholysis, please consult a licensed and sanitary nail professional, physician, and/or podiatrist. There are medications and over the counter topical agents that can be given or suggested to prevent further separation and/or generate new nail growth. 
