A persistent fungal infection of the skin and nails may be the cause of persistent itching accompanied by yellow, thick, uneven, or black nails. Onabet may provide short-term relief, but if cream is the only treatment, nail fungal infections frequently recur. A black nail should be closely examined since it may be caused by an injury, a significant infection, or, in rare cases, another dangerous ailment. For a nail check and potential fungal test, please see a dermatologist. If you have diabetes, you may need to take antifungal medications for a longer period of time, take good care of your nails, and keep your skin dry.