I have a toenail fungus that just won’t go away. What can I do?

DEAR DOCTOR K: I have a toenail fungus that just won't go away. What can I do?
DEAR READER: Fungal toenail infections occur when a fungus infects the area under the surface of a toenail. Fungi love warm, damp environments, and the space inside our shoes provides the perfect habitat. As the infection takes hold, it creates a strong, unpleasant odor. The toenail thickens and turns yellowish-brown. Eventually the nail may separate from the nail bed. Fungal infections are notoriously difficult to get rid of, but there are things you can do to stop their spread and improve your toenail's appearance.