A fungal infection of the nail is called Onychomycosis and is a fairly common condition affecting the nails. It often is seen as a white or off-white spot on the nail and sometimes the discolouration can be black or even greenish. The nail becomes brittle, dull or sometimes loosened from the nail bed. It takes a long time to heal even with medications. Toe nail fungus infections are commoner than finger nail fungus.