A fungal infection, typically on the toenails, is the most common nail disorder. People with diabetes, those who wear tight-fitting shoes and those who get a lot of manicures or pedicures are most susceptible. An infected nail will be painful and discolored, with a brownish-black band. The nail also might show scars, pits, ridges or lesions. Anti-fungal medication can treat the nail. To avoid infection, keep toenails short, discard old footwear and dont go barefoot around public showers and pools.