Onychomycosis is a fungal infection that affects the nails, commonly seen in the toenails but can also occur in fingernails. It is characterized by changes in nail color, thickness, and texture, often leading to nail brittleness and separation from the nail bed. The infection can be caused by various fungi, including dermatophytes, yeasts, and non-dermatophyte molds. Treatment options for onychomycosis include topical antifungal medications, oral antifungal drugs, and in some cases, surgical removal of the affected nail. Prevention strategies involve maintaining good foot hygiene, keeping nails trimmed, and avoiding damp environments where fungi thrive.