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.1 The fungal organism that is responsible for most fungal nail infections is Trichophyton rubrum.2 The medical terms for this type of fungal infection are onychomycosis or tinea unguium.
What It Looks Like
There are four different types of onychomycosis and they are classified by the part of the nail that is involved. 3The 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 onychomycosis.4 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.
The following are instances that either promote a fungal infection or encourage the growth of fungi.
Tight footwear promotes a 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 Onychomycosis
Not every thickened, discolored nail is a fungal infection. Other diseases that can cause thickened nails are psoriasis, eczema, and lichen planus.5 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 that are used to diagnose a fungal nail infection:6
The KOH test
A fungal culture
The KOH test has the advantage that it can be quickly performed. A fungal culture takes three to four weeks to come back but can identify the exact fungal organism, if there is any question.
Three Types of Treatment
The treatment of onychomycosis is expensive and long-term. It requires a commitment on the part of the patient to take medicine for several months.
Unfortunately, topical preparations (medications that you apply to the nail area) 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.7 It may be an option, however, for people who cannot take oral antifungal medications (pills that you take by mouth).
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.8
All three medications have significant side effects and interact with many medications. Anyone taking oral antifungal medications must have periodic lab tests 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)9 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 milligrams once a day for six weeks for fingernail infections and 12 weeks for toenail infections.
Itraconazole (Sporanox)10 is also FDA-approved to treat onychomycosis 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 milligrams once a day for six weeks for fingernail infections and 12 weeks for toenail infections. The pulse dosing is 200 milligrams twice a day for one week per month, repeated for two or three months.
Fluconazole (Diflucan)11 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 needs to be taken only weekly. Initial studies show that fluconazole is 72 to 89 percent effective. The dosage used is 450 milligrams once a week for four to nine months.
A Word From Verywell
If you or a loved one has a fungal nail infection, you are not alone. In fact, onychomycosis affects up to 10 percent of the general population. Men are more likely to get them than women, and the likelihood of developing one increases with age. That being said, be sure to undergo a proper diagnosis, either by your primary care provider or by a dermatologist (a doctor who specializes in treating the skin and nails).