Nail Fungus, or onychomycosis, is a common infection of the fingernails or toenails by a fungus. It is more common in the toenails than the fingernails and can occur as a result of repeated trauma or excessive warmth and moisture. Bathing in communal areas and sharing nail clippers can lead to fungal infection. It causes hardening and often yellow discoloration of the nails and makes them difficult to trim and sometimes painful. Hardened discolored nails are not always due to a fungus and a nail culture can be done in order to confirm fungal infection prior to treatment. Topical treatment can be applied to the affected nails but is not always effective. Even when effective, it takes several months for nails to grow back normally, regardless of the type of treatment. Oral medication can also be used to treat nail fungus.