Encyclopedia / O / Onychomycosis



Mycosis is any disease caused by a fungus. Onychomycosis is infection of the toenail with fungus.


Skin fungi not only can disfigure the nails but can also cause physical pain and impair the ability to work. Nail fungi affect toenails four times more often than fingernails. Once fungi take hold, it may spread from nail to nail, foot to foot, and rarely to the hands and fingernails.

When the nails are exposed to a warm moist environment, a fungus can develop on the nail or under its outer edge. This is called onychomycosis. Depending on the type of fungus, the nail may turn yellow, gray, brown, or black. The nail may become brittle and crack. It may separate from its bed. The surrounding skin may be red, itchy or swollen.

There are a number of types of fungal infections.

DSO (distal subungual onychomycosis): This is where the fungus, usually a dermatophyte, invades the space between the tip of the toe and the nail tip or the skinfolds at the sides of the nails. The toenails turn yellow and separate from the nail bed beneath them.

WSO (white superficial onychomycosis): Less common than DSO, this affects only the surface of the nail turning it white and crumbly in spots or all over the nail surface. This is the most easily treated infection in that it can be simply scraped off the nail and a topical antifungal medication applied.

PSO (proximal subungual onychomycosis): This is the least common of nail fungi and may first appear as a white or yellowish spot on the nail close to the cuticle. From there, it can progress into a plaque that collects on the underside of the nail. Then, debris may collect under the nail and it may lift off its bed and even be shed entirely. This infection is usually treated with a systemic drug.

Candida Albicans (yeast infection): This more commonly affects fingernails than toenails. The infection can turn nails yellow or green or the nail may look opaque. This infection can be treated topically.


Topical ointments and antifungal powders may help contain a fungus infection, but they will not cure most cases of DSO, PSO and stubborn yeast infections (candida albicans). In cases of pain or discomfort, treatment becomes necessary.

The standard treatment for fungal toenail infection has been the oral drug griseofulvin. This prevents the fungus from spreading until the infected nail grows out. Another drug commonly used is ketoconazole. Treatment can, however, take many months and the drugs have side effects that can be serious.

Several new drugs have been approved. These are itraconazole (Sporanox) and fluconazole (Diflucan). These were originally developed to treat fungal infections in AIDS patients and those with compromised immune systems. Unlike griseofulvin, these newer drugs are absorbed into the blood at sufficiently high levels to penetrate the nail and destroy the fungus. The infection usually clears within eight months. Side effects are minor and may involve occasional headaches or digestive upset. The drugs are, however, expensive.

Yet another drug has been shown to be effective in treating fungal toenail infection. This is terbinafine and is available as a topical cream called Lamisil. In some studies, terbinafine has achieved an 80 percent cure rate in toenail infections when given orally on a daily basis for only three months.

Additionally, a new nail lacquer, ciclopirox (Penlac), was recently approved to treat finger or toenail fungus that does not involve the white portion of the nail (lunula) in patients that do not have immune deficiency.

The newer drugs are more effective than griseofulvin and ketoconazole and they require much shorter courses of treatment to work.


What type of fungal infection is it?

Can this be treated with a topical medication?

Will oral medication be prescribed?

Which drug will you prescribe?

What are the side effects?

How long will it take to cure the infection?

Can a recurrence be prevented?

To prevent fungal growth, it is advisable to:

  • Keep the nails dry and clean
  • Change socks often, even several times a day if necessary
  • Use an antifungal foot spray or powder
  • Avoid cutting or tearing the skin around the toenails since this may be an entry point for infection