What Is Toenail Fungus?

Onychomycosis — commonly known as toenail fungus — is a fungal infection of the nail plate, nail bed, or nail matrix caused most commonly by dermatophyte fungi (particularly Trichophyton rubrum and T. mentagrophytes), less frequently by non-dermatophyte molds, and occasionally by yeasts such as Candida. It is the most common nail disorder, affecting an estimated 10% of the general population and up to 50% of people over age 70. While toenail fungus is rarely dangerous in healthy individuals, it causes significant cosmetic embarrassment, can become painful as nails thicken, and serves as a potential reservoir for spread to other nails, skin (tinea pedis/athlete’s foot), and family members.

Onychomycosis is notoriously difficult to eradicate because the fungus resides within and under the nail plate — a location that topical treatments penetrate poorly and that provides a protected environment for fungal regrowth. Understanding the available treatment options and their respective efficacy rates helps patients make informed decisions in partnership with their podiatrist.

Recognizing Toenail Fungus

Fungal nail infection typically begins at the free edge or lateral borders of the nail and progresses proximally toward the nail root. The nail becomes discolored (yellow, brown, white, or black), thickened, brittle, and may separate from the underlying nail bed (onycholysis). As infection progresses, debris accumulates under the nail (subungual hyperkeratosis), the nail may crumble, and the nail plate can become grossly distorted. Some patients experience pain, particularly when wearing closed footwear, and the thickened nail can press on adjacent toes.

Not all nail discoloration is fungal. Nail trauma (subungual hematoma), psoriasis affecting the nail (nail psoriasis), lichen planus, and bacterial infections can produce similar appearances. Accurate diagnosis before initiating treatment is important — oral antifungals are not indicated for non-fungal nail disease. Your podiatrist can take nail clippings for fungal culture and microscopy (KOH preparation) to confirm the diagnosis before prescribing treatment.

Oral Antifungal Medications

Oral terbinafine (Lamisil) is the most effective treatment for dermatophyte onychomycosis, with cure rates of 70–80% in clinical trials. The standard course is 250 mg daily for 12 weeks for toenail infection. Terbinafine incorporates into the nail plate and remains active for months after the treatment course ends. Potential side effects include gastrointestinal upset (usually mild) and, rarely, hepatotoxicity — liver function tests are sometimes checked before and during treatment, particularly for patients with pre-existing liver conditions or who are on multiple medications. Itraconazole (Sporanox) is an alternative, available in pulse dosing regimens, and is effective against both dermatophytes and Candida. Fluconazole is a third option sometimes used weekly for prolonged periods.

Oral antifungals require patience — because they work by allowing the new, drug-infused nail to grow out while the infected nail grows off the end, clinical cure (a fully normal-appearing nail) may not be evident until 12–18 months after starting treatment, as toenails grow very slowly. Recurrence rates after oral treatment are significant — approximately 20–25% — because reinfection from shoes, socks, and environmental sources is common without preventive measures.

Topical Antifungal Treatments

Prescription topical antifungals offer a treatment option for patients who cannot take oral medications due to drug interactions, liver disease, or personal preference. Efinaconazole 10% solution (Jublia) and tavaborole 5% solution (Kerydin) are newer prescription topicals that penetrate the nail plate better than older formulations. Applied daily to affected nails, they achieve complete cure in approximately 15–18% of patients at 52 weeks — significantly lower than oral terbinafine, but with a much more favorable side effect profile. They are best suited for mild-to-moderate infections affecting a limited number of nails, or as maintenance therapy after oral treatment to reduce recurrence. Ciclopirox lacquer (Penlac) is an older topical with lower nail penetration and efficacy rates around 5–8% for complete cure.

Laser Treatment for Toenail Fungus

Laser therapy for onychomycosis uses targeted light energy to penetrate the nail plate and destroy fungal organisms through thermal effects, without harming surrounding tissue. Multiple laser systems have been studied, including Nd:YAG (1064 nm) and diode lasers. Laser treatment is painless or causes only mild warming sensations, requires no systemic medication, and carries no risk of drug interactions or liver effects. Published studies show mycological cure rates (confirmed negative cultures) of 30–50% with multiple treatments, though independent studies tend to show lower rates than manufacturer-sponsored research.

Laser treatment is typically performed as a series of 3–4 sessions at 6–8 week intervals. While not covered by most insurance plans, laser therapy is an attractive option for patients who cannot take oral antifungals, prefer to avoid systemic medication, or have had recurrence after oral treatment. Combining laser treatment with topical antifungal therapy may enhance outcomes.

Preventing Recurrence

Treatment of toenail fungus is only half the battle — preventing reinfection is equally important. Antifungal powder or spray applied to shoes and socks eliminates the fungal reservoir in footwear. Replacing old shoes that harbor fungal spores after successful treatment prevents immediate reinfection. Wearing moisture-wicking socks, drying feet thoroughly after bathing (especially between the toes), and avoiding walking barefoot in public showers, locker rooms, and pool areas reduces reexposure. Trimming nails straight across and keeping them short reduces the subungual space where fungi accumulate. Patients who have had toenail fungus should also treat any concurrent athlete’s foot (tinea pedis) on the skin, as it serves as a source for nail reinfection.

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Dr. Tom Biernacki, DPM

Dr. Tom Biernacki, DPM is a double board-certified podiatrist and foot & ankle surgeon at Balance Foot & Ankle Specialists in Southeast Michigan. With over a decade of clinical experience, he specializes in heel pain, bunions, diabetic foot care, sports injuries, and minimally invasive surgery. Dr. Biernacki is a member of the APMA and ACFAS, and his patient education content on MichiganFootDoctors.com and YouTube has reached over one million views.