Fungal Nail: A toenail that becomes infected with fungus may become thickened, discolored, brittle and hard. The dark, enclosed, and often sweaty environment of shoes makes toenail fungus common in our society. Athlete's foot (fungus of the skin) is common for the same reasons. Several treatment options are available (depending on the severity of the problem)and include nail trimming, topical antifungal medications, oral antifungals, and surgical nail care.