Overview of Fungal Nail Infections

Don't assume you have a fungal infection, as there are lots of mimickers.

Many people have thickened, discolored toenails and fingernails, and about 50 percent of these abnormal nails are due to a fungal infection of the nail bed, matrix, or nail plate. The fungal organism responsible for most fungal nail infections is Trichophyton rubrum.

The medical terms for this type of fungal infection are onychomycosis or tinea unguium.

Appearance of Fungal Nail Infections

There are actually four different types of fungal nail infections classified by the part of the nail involved.

The most common infection involves the end of the nail when the fungi invade the hyponychium.

Initially, the nail plate splits from the nail bed, a process called onycholysis. Then, the end of the nail turns yellow or white and keratin debris develops under the nail causing further separation. The fungus then grows in the nail causing it to become fragile and crumble. 

Risk Factors for Fungal Nail Infections

The following are instances that either promote infection with fungi or encourage the growth of fungi:

  • Tight footwear promotes crowding of the toes, keeping the toes warm and moist—a perfect environment for fungi to grow.
  • Exercise may cause repeated minor trauma to the hyponychium, allowing fungi to invade.
  • Communal showers can expose the feet to fungi.
  • Diseases that influence the immune system like AIDS and diabetes can make it easier for a fungal infection to start.

Diagnosis of Fungal Nail Infections

Not every thickened, discolored nail is a fungal infection.

Other diseases that can cause thickened nails are psoriasis, eczema, and lichen planus. It is important that fungal nail infections are diagnosed properly because treatment is long-term and expensive.

Fungal nail infections are diagnosed by taking a sample of the debris under the nail. The most fungal elements are found under the nail and closest to the skin, therefore the nail should be trimmed before a sample is taken.

There are two tests used to diagnose a fungal nail infection:

The KOH test has the advantage that it can be quickly performed. A fungal culture takes 3 to 4 weeks to come back but can identify the exact fungal organism, if there is any question.

Treatment of Fungal Nail Infections

The treatment of fungal nail infections is expensive and long-term. It requires a commitment on the part of the patient to take medicine for several months. Unfortunately, topical preparations do not effectively treat fungal nail infections.

The FDA has approved a nail lacquer named ciclopirox (Penlac) for fungal nail infections, but it is seldom effective. It may be an option, however, for people who cannot take oral antifungal medications.

There are three effective oral antifungal medications—two that are FDA approved for fungal nail infections and one that is not FDA approved specifically for nail infections.

All three medications have significant side effects and interact with many medications.

Anyone taking oral antifungal medications must have periodic labs done to monitor liver and blood cell function. The oral antifungal medications are incorporated into the nail—therefore, they continue to work even after the medication is discontinued. None of the oral antifungals can be taken during pregnancy.

  • Terbinafine (Lamisil) is FDA approved to treat fungal nail infections and is 70 to 90 percent effective when used as prescribed. Terbinafine does interact with a few other medications, most notably caffeine and cimetidine. The dosage used is 250 mg once a day for 6 weeks for fingernail infections and 12 weeks for toenail infections.
  • Itraconazole (Sporanox) is also FDA approved to treat fungal nail infections and is 70 to 80 percent effective. Itraconazole interacts with many medications and should be taken with food. Itraconazole can be taken daily or as pulse therapy. The daily dose is 200 mg once a day for 6 weeks for fingernail infections and 12 weeks for toenail infections. The pulse dosing is 200 mg twice a day for one week per month repeated for 2 or 3 months.
  • Fluconazole (Diflucan) is not FDA approved to treat fungal nail infections but is an effective oral antifungal medication. The advantage of fluconazole is that it stays in the body for a long time and only needs to be taken weekly. Initial studies show that fluconazole is 72 to 89 percent effective. The dosage used is 450 mg once a week for 4 to 9 months.

A Word From Verywell

If you or a loved one have a nail fungal infection, you are not alone. In fact, fungal infections of the nail affect up to 10 percent of the general population. Men are more often affected than women, and the likelihood of developing one increases with age. That being said, be sure to undergo a proper diagnosis, often by a dermatologist. 


Thomas J, Jacobson GA, Narkowicz CK, Peterson GM, Burnet H, Sharpe C. Toenail onychomycosis: an important global disease burden. J Clin Pharm Ther. 2010 Oct;35(5):497-519.

Westerberg DP, Voyack MJ. Onychomycosis: Current Trends in Diagnosis and Treatment. Am Fam Physician. 2013 Dec 1;88(11):762-70.

Continue Reading