What is toenail fungus?

Toenail fungus (also called onychomycosis) is a nail disorder that affects nearly 20% of the population. Toenail fungus usually begins in a small space between the end of the nail and the nail bed, where soft yellow material gradually develops.

As the disorder develops, the nail becomes thick and yellow and may show white spots and streaks. If toenail fungus is left untreated, the nail can eventually grow fragile, chalky, or crumbly. In more severe cases, the nail may crumble away.

What causes toenail fungus?

Toenail fungus is commonly caused by:

  • Damage to the nail
  • A warm, moist shoe environment
  • Tight-fitting shoes
  • Walking barefoot in public areas

Last reviewed by a Cleveland Clinic medical professional on 01/06/2017.


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