Toenail fungus is an infection underneath the surface of the nail caused by fungus. Over time toenail fungus can change the appearance of the nail, such as a causing brownish discoloration and/or thickening of the nail. Another symptom of toenail fungus that can be embarrassing is bad foot odor caused by subungal (under the nail) fungal debris. Also, fungal shedding from the nail can spread...