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Onychomycosis (nail fungus) is the most common infection of the nails in adults; it affects toenails more frequently than fingernails. Usually, the first sign of onychomycosis is a white or yellow spot under the nail. Left untreated, onychomycosis causes a nail to thicken and become brittle. The nail may split or crumble, or even separate from the nail bed. Onychomycosis can be contagious, spreading from nail to nail or, rarely, to nearby skin.

Treatment of onychomycosis can be difficult because the infection is deeply embedded within the nail. Even after successful treatment, to again look normal, the nail must completely grow out; the damaged part of the nail cannot be restored.

Risk Factors for Onychomycosis

A common risk factor for onychomycosis is aging, in part because older people have diminished blood circulation, and have had a longer exposure to the fungus. Other risk factors for onychomycosis include the following:

  • Being male
  • Having a family history of nail fungus
  • Sweating a great deal
  • Walking barefoot in humid or moist surroundings
  • Having psoriasis or athlete's foot
  • Having a minor skin or nail injury
  • Being diabetic or having circulatory problems

Having a weakened immune system is also a risk factor for onychomycosis.

Symptoms of Onychomycosis

The first symptom of onychomycosis is usually an abnormal appearance of the nail, which thickens and changes color to white, yellow, green or black. Other symptoms of onychomycosis include:

  • Brittle, split, ragged or crumbling nails
  • Nails with distorted shape
  • Dull, lusterless nails
  • Pain in the toes or fingertips
  • Nails that emit a slightly foul odor

Onychomycosis can cause a nail to become so thick that it interferes with standing, walking and exercising.

Treatment of Onychomycosis

Because of the possibility of permanent damage, nail fungus should be treated promptly. Topical over-the-counter medications are widely available in powder, ointment and nail-polish forms, but should only be used when less than half of the nail is damaged, or when oral medication is not an option. Because they cannot penetrate the nail deeply enough, topical medications rarely eradicate onychomycosis. They may, however, be appropriate for use in combination with oral medications.

Oral medications are more effective than topical ones because they quickly spread throughout the body and penetrate the nail plate. In severe cases of onychomycosis, the nail may be removed either chemically or surgically. Doing so does not cure onychomycosis, however; removal must be combined with the use of oral medication to be effective.