Nail Fungus (Toenail Fungus): Causes, Symptoms & Treat

Table of Contents

• What Is Nail Fungus?
• Symptoms
• Causes & Risk Factors
• Treatment Options
• When to See a Podiatrist
• Frequently Asked Questions

If your toenail has turned yellow, thickened, or started crumbling at the edges, you know how frustrating — and embarrassing — nail fungus can be. Sandal season rolls around and you find yourself hiding your feet. You’re not alone: onychomycosis affects an estimated 14% of adults in North America, and we treat it every single week in our clinic.

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What Is Nail Fungus?

Nail fungus — medically called onychomycosis — is an infection caused by dermatophytes, yeasts, or molds that invade the nail plate and nail bed. The infection starts at the free edge or the sides of the nail and gradually works its way toward the base. In our clinic, the most common culprit is Trichophyton rubrum, the same organism responsible for athlete’s foot.

Without treatment, the infection deepens and becomes harder to eradicate. The nail matrix (the growth center) can become involved, leading to permanent nail damage. A 2024 review in the Journal of the American Academy of Dermatology found that spontaneous resolution without treatment occurs in less than 5% of cases.

Symptoms of Nail Fungus

Nail fungus is often mistaken for nail trauma or psoriasis, so knowing the full symptom picture matters. Watch for any combination of these signs in one or more toenails:

• Yellow, brown, or white discoloration — often starts at the tip
• Thickening of the nail — becomes difficult to trim
• Brittle, crumbly, or ragged edges
• Separation from the nail bed (onycholysis)
• Debris buildup under the nail (subungual hyperkeratosis)
• Mild odor from the nail area
• Distorted nail shape as the infection progresses

Pain is uncommon early on but can develop if the thickened nail presses against your shoe. We’ve seen patients develop blisters and even ulcers from the pressure — particularly in diabetic patients whose sensation is reduced.

What Causes Nail Fungus?

Nail fungus thrives in warm, moist environments and enters through tiny separations between the nail and skin. The most common cause we identify in our clinic is untreated athlete’s foot that spreads to the toenail. Risk factors that significantly raise your chances include: age over 60, diabetes, peripheral vascular disease, a weakened immune system, sweaty feet, tight-fitting shoes, walking barefoot in communal areas, and a family history of the condition.

Nail Fungus Treatment Options

Treatment success depends on how much of the nail is affected and which organism is responsible. We always culture the nail first to confirm fungal infection before prescribing systemic medication. Here’s the treatment ladder we use at Balance Foot & Ankle:

• Topical antifungals (efinaconazole, tavaborole, ciclopirox) — best for mild, distal infections; apply daily for 48 weeks
• Oral terbinafine — 12-week course, most effective treatment with ~70% mycological cure rate per a 2023 meta-analysis
• Laser therapy — adjunct treatment, no oral medication required; results in 6–12 months
• Nail debridement — mechanical thinning reduces fungal load and improves topical penetration
• Nail avulsion — removal of severely infected nail in refractory cases

The most common mistake we see is stopping treatment once the nail “looks better.” Fungal infections live deep in the nail plate and require the full treatment course — typically 6–12 months until a completely clear nail grows in.

Frequently Asked Questions

Is nail fungus contagious? Yes — it can spread person-to-person through shared showers, towels, or nail tools. Always use flip-flops in public pools and locker rooms, and never share nail clippers.

Can I treat nail fungus at home? Mild cases may respond to OTC topical antifungals, but the cure rate is significantly lower than prescription options. Home remedies like tea tree oil or Vicks VapoRub have limited evidence and should not replace medical treatment for moderate-to-severe infections.

How long does treatment take? Toenails grow slowly — even after the fungus is eliminated, it takes 12–18 months for a completely clear nail to grow in. Fingernails clear faster, in 6–9 months.

The Bottom Line

Nail fungus is common, stubborn, and almost never clears without proper treatment. The earlier you address it, the better the outcome. If you’re noticing yellow, thickened, or crumbling toenails, our team at Balance Foot & Ankle can culture the nail, confirm the diagnosis, and recommend the most effective treatment for your specific infection — without unnecessary guesswork.

Sources

• Gupta AK et al. Onychomycosis epidemiology. JAAD 2024.
• Lipner SR. Oral terbinafine meta-analysis. JAMA Dermatol 2023.
• Elewski BE. Onychomycosis pathogenesis. NEJM 2022.

Related Care at Balance Foot & Ankle

Clinical toenail services at our Howell and Bloomfield Hills offices.

Ingrown Toenail TreatmentToenail MatrixectomyMedical Pedicure

Considering home remedies? Read our evidence review: Does Listerine Work for Toenail Fungus? — Michigan podiatrist breaks down the evidence and correct technique.

Experiencing a painful soft corn between your toes? See our guide: Heloma Molle (Soft Corn) — Michigan podiatrist explains causes and the 4 most effective treatment options.

Frequently Asked Questions About Nail Fungus

Many patients ask if Vicks works for nail fungus before trying prescriptions. See our guide: The Truth About Vicks VapoRub for Toenail Fungus — Michigan podiatrist reviews the clinical evidence and explains what Vicks can realistically achieve.