Fungus Toenails

Fungal nail infection (Onychomycosis) is an infection of the nails by a fungus.

Causes, incidence, and risk factors

The body normally hosts a variety of bacteria and fungi. Some of these are useful to the body. Others may multiply quickly and form infections. Fungi can live on the dead tissues of the hair, nails, and outer skin layers.

Fungal infections include mold-like fungi that cause:

  • Athlete’s foot
  • Jock itch
  • Ringworm on the skin of the body or head

Fungal nail infections are most often seen in adults. They often follow fungal infection of the feet. Toenails are affected more often than fingernails. People who often go to public swimming pools, gyms, or shower rooms, and people who sweat a great deal, often have mold-like infections. The fungi that cause them thrive in warm, moist areas.

The following increase the risk of a fungal infection:

  • Getting manicures and pedicures using utensils that have been used on other people
  • Getting minor skin or nail injuries
  • Having a nail deformity or nail disease
  • Having moist skin for a long timePoorly functioning immune system
  • Wearing closed-in footwear


  • Nail changes on one or more nails (usually toenails):
  • Brittleness
  • Change in nail shape
  • Crumbling of the outside edges of the nail
  • Debris trapped under the nail
  • Loosening or lifting up of the nail
  • Loss of luster and shine
  • Thickening of the nail
  • White or yellow streaks on the side of the nail

Signs and tests

Your doctor will suspect a fungal infection based on the appearance of the nails. The diagnosis can be confirmed by scraping the nail and:

  • Looking at it under a microscope to identify the type of fungus
  • Sending it for a culture (however, it may take up to 3 weeks to get results)