The Bottom Line

Toenail fungus (onychomycosis) is the most common nail disease in adults, affecting about 10% of the general population and up to 50% of people over age 70. It causes nails to become thick, yellow, crumbly, and sometimes painful. It does not go away on its own. Oral antifungal pills (terbinafine or itraconazole) have the best cure rates — around 70–80% — but treatment takes months and requires patience. See a dermatologist early, because the longer it goes untreated, the harder it is to clear.

What Is Toenail Fungus?

Onychomycosis is a fungal infection of the nail. It most often affects toenails, but fingernails can also be infected. The fungi responsible are called dermatophytes — the same family of fungi that cause athlete's foot and ringworm. In some cases, yeasts (like Candida) or molds cause nail infections too.

The infection starts when fungi enter through a tiny gap between the nail plate and the nail bed — often through a small cut, a crack in dry skin, or through repeated pressure on the tip of the toe from shoes. Once inside, the fungi feed on keratin, the protein that makes up your nails, and slowly spread.

Onychomycosis accounts for about half of all nail disorders seen by dermatologists. It is more frequent in older adults, in people with diabetes, and in anyone with circulation problems or a weakened immune system.

What Does It Look Like?

The classic signs of toenail fungus include:

  • Yellow, white, or brown discoloration — often starting at the tip of the nail and spreading back toward the base
  • Thickening of the nail — the nail becomes harder and more difficult to trim
  • Crumbling or brittle edges — the nail breaks apart easily, especially at the tip
  • Separation from the nail bed (onycholysis) — the nail lifts away from the underlying skin
  • Debris under the nail — a buildup of white or yellow powdery material
  • Distorted shape — the nail becomes irregular or warped

In most cases, there is no pain early on. Pain and tenderness can develop when the nail becomes very thick or puts pressure on adjacent toes inside a shoe.

What Causes It and Who Is at Risk?

Fungi thrive in warm, moist environments. You are more likely to develop toenail fungus if you:

  • Walk barefoot in public showers, locker rooms, or pools
  • Wear tight shoes that trap moisture and heat
  • Have athlete's foot (tinea pedis) — the fungus can spread from skin to nails
  • Have diabetes, poor circulation, or a weakened immune system
  • Are over age 60 (older nails grow more slowly and have more micro-separations)
  • Have a family history of nail fungus (genetic susceptibility is real)
  • Experience repeated nail trauma — athletes and runners are especially affected

Men are about twice as likely as women to develop onychomycosis. People with HIV or on immunosuppressive medications are at particularly high risk.

How Is It Diagnosed?

Many conditions can make nails look thick, yellow, or crumbling — including nail psoriasis, trauma, and contact dermatitis. A dermatologist will usually confirm the diagnosis before prescribing antifungal treatment. Confirmation typically involves:

  • Nail clipping or scraping — debris from under the nail is sent to a lab for KOH microscopy or fungal culture
  • PAS stain — a special stain on a nail sample that is more sensitive than standard culture
  • PCR testing — newer, highly accurate molecular test that identifies the specific fungus

Getting a confirmed diagnosis matters because oral antifungal medications have potential side effects, and there is no point taking them if the problem is not actually fungal.

Treatment Options

Oral Antifungals (Best Cure Rates)

Terbinafine (Lamisil) is the most effective treatment, with cure rates of 70–80%. You take one pill daily for 6 weeks (fingernails) or 12 weeks (toenails). The medication stays in the nail for months after you stop taking it. Terbinafine works best against dermatophytes, the most common type of nail fungus.

Itraconazole (Sporanox) is an alternative, often prescribed in pulse therapy — one week on, three weeks off, for 2–3 cycles. It covers a broader range of fungi including yeasts. Cure rates are about 50–70%.

Both medications require a blood test to check liver function, though serious liver problems are rare (fewer than 1 in 1,000 patients). Your doctor will review your other medications for potential interactions.

Topical Antifungals (Mild/Early Disease)

Prescription nail lacquers work for superficial infections or as add-on therapy:

  • Efinaconazole 10% solution (Jublia) — applied daily for 48 weeks; complete cure rates around 15–18%, but significantly better than placebo
  • Tavaborole 5% solution (Kerydin) — similar application and cure rates
  • Ciclopirox 8% nail lacquer (Penlac) — older option, lower penetration through the nail plate

Topical treatments work best when the infection is limited to the top portion of the nail and the nail matrix (base) is not involved. They are a good option for people who cannot take oral medications.

Laser Treatment

Several laser systems (Nd:YAG, diode, CO2) can heat and disrupt fungal organisms in the nail. Studies show improvement in nail appearance in many patients, but complete mycological cure rates remain lower than oral antifungals. Multiple sessions are typically needed.

What to Expect During Treatment

Even after successful treatment, your nail will not look normal right away. Toenails grow very slowly — about 1–1.5 mm per month — so a toenail takes roughly 12–18 months to fully grow out and replace itself. Recurrence is common — fungal nail infections return in about 20–25% of successfully treated patients within one year. Prevention habits are essential after treatment.

When to See a Dermatologist

  • You have a thickened, discolored, or crumbling nail that has not improved on its own
  • You have diabetes or circulation problems — nail infections can lead to secondary bacterial infections and serious complications
  • Your nail is painful or causing problems with footwear
  • Over-the-counter treatments have not worked after several months
  • You are unsure whether your nail problem is fungal or something else (such as psoriasis)
  • You want to start oral antifungals and need lab work and monitoring

Prevention Tips

  • Keep feet clean and dry; dry thoroughly between toes after bathing
  • Wear moisture-wicking socks and rotate shoes to allow them to dry out completely
  • Wear flip-flops or shower shoes in public locker rooms, pools, and showers
  • Trim nails straight across, keep them short, and avoid cutting too deep
  • Treat athlete's foot promptly — it is a reservoir for nail infection
  • Avoid sharing nail clippers, files, or footwear

Frequently Asked Questions

Is toenail fungus contagious?

Yes — moderately. You can spread it to other nails on your own feet, and it can be transmitted to family members through shared bathrooms, towels, or nail tools. Most healthy adults who are exposed do not develop an infection, but people with diabetes or immune suppression are at higher risk.

Can I treat toenail fungus without seeing a doctor?

Over-the-counter topical products are available, but their effectiveness for established toenail fungus is limited. Prescription medications — especially oral terbinafine — are far more effective. Seeing a dermatologist also ensures you get the correct diagnosis, because not all nail changes are due to fungus.

How long does it take for the nail to look normal after treatment?

Even after the fungus is cleared, you need to wait for the new, healthy nail to grow in. This typically takes 12–18 months for toenails. The infection is gone, but the damaged nail plate still has to grow out completely.

Will the fungus come back?

Recurrence is common — roughly 20–25% of patients within the first year. Using preventive measures consistently after treatment (keeping feet dry, rotating shoes, treating athlete's foot early) significantly reduces the chance of relapse.

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Trusted Resources

Always consult a board-certified dermatologist for diagnosis and personalized treatment recommendations. This article is for educational purposes only.