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Fungal Toenail Infection (Onychomycosis)

Overview

Onychomycosis, commonly called a fungal toenail infection, is a condition in which fungi (most often dermatophytes, yeasts, or molds) invade the nail plate, nail bed, or surrounding skin. The infection leads to thickened, discoloured, and often brittle nails.

While anyone can develop onychomycosis, it is most prevalent in adults > 40 years old, especially men. According to the CDC, up to 10‑14 % of the U.S. population is affected, and the prevalence rises to 20 % in people over 60 years of age.

The condition is not life‑threatening, but it can cause pain, cosmetic concerns, and secondary bacterial infections, particularly in people with diabetes or compromised immune systems.

Symptoms

Symptoms develop slowly over months and can vary by the type of fungus and extent of infection.

• Discolouration – nails become white, yellow, brown, or black.
• Thickening – the nail plate may become noticeably thicker than adjacent nails.
• Brittle or crumbly texture – the nail may break easily or develop ragged edges.
• Distortion of nail shape – the nail may lift (onycholysis) or become misshapen.
• Foul odour – a musty smell can arise from the infected nail or surrounding skin.
• Pain or discomfort – especially when pressure is applied (e.g., wearing shoes).
• Staining of surrounding skin – the skin under the nail may become red or inflamed.
• Spread to other nails – untreated infection often spreads to adjacent toes or fingernails.

Causes and Risk Factors

What causes onychomycosis?

The infection is caused by a group of fungi that thrive in warm, moist environments:

• Dermatophytes (most common – Trichophyton rubrum, T. interdigitale).
• Yeasts – especially Candida albicans, more common in people with diabetes or immunosuppression.
• Molds – less common, usually in people with chronic nail trauma.

Fungi invade the nail through tiny cracks in the nail plate, nail bed, or surrounding skin.

Who is at higher risk?

• Age > 40 years (reduced nail growth rate & poorer circulation).
• Male gender (higher prevalence, possibly due to footwear habits).
• People with diabetes, peripheral vascular disease, or immune compromise.
• History of athlete’s foot or other skin fungal infections.
• Frequent use of communal showers, pools, or locker rooms.
• Tight, non‑breathable footwear that promotes moisture.
• Nail trauma (e.g., from sports, poorly fitting shoes).
• Conditions that cause nail thickening (psoriasis, eczema).
• Use of artificial nails or nail polish that traps moisture.

Diagnosis

Because nail changes can mimic psoriasis, trauma, or lichen planus, an accurate diagnosis is essential.

Clinical examination

• Visual inspection of nail colour, thickness, and shape.
• Assessment of surrounding skin for tinea pedis (athlete’s foot).

Laboratory tests

1. Potassium hydroxide (KOH) preparation – a nail clipping is placed on a slide with KOH to dissolve keratin; fungal hyphae become visible under a microscope.
2. Fungal culture – the sample is placed on a special medium and incubated for 2–4 weeks to identify the specific organism.
3. Histopathology with periodic acid‑Schiff (PAS) stain – a biopsy of the nail bed can reveal fungal elements when microscopy is inconclusive.
4. Polymerase chain reaction (PCR) – increasingly used for rapid, species‑specific identification.

Guidelines from the CDC recommend confirming the diagnosis with a lab test before initiating systemic therapy, because oral antifungals carry significant side‑effects.

Treatment Options

Therapy depends on the extent of disease, patient health, and cosmetic concerns. Options fall into three categories.

1. Oral antifungal medications

Medication	Typical Dose	Duration	Key Safety Notes
Terbinafine (Lamisil)	250 mg daily	12 weeks (toenails)	Liver‑function monitoring; drug‑interaction potential.
Itraconazole (Sporanox)	200 mg twice daily 1 week/month	12 weeks (pulsed)	May cause heart failure exacerbation; monitor liver enzymes.
Fluconazole (Diflucan)	150‑200 mg weekly	6‑12 months	Generally well‑tolerated; watch for drug interactions.

Oral agents have the highest cure rates (70‑80 %) but require baseline liver function tests and periodic monitoring.

2. Topical therapies

• Efinaconazole 10 % solution (Jublia) – applied daily to the affected nail for 48 weeks. Cure rates ~15‑18 % but useful for mild disease or patients who cannot take oral drugs.
• Tavaborole 5 % solution (Kerydin) – similar regimen, cure rates ~7‑10 %.
• Ciclopirox 8 % lacquer (Penlac) – requires daily application for up to a year; modest efficacy (≈10 %).

Topicals are often combined with debridement (nail filing) to improve penetration.

3. Mechanical and procedural interventions

• Nail debridement – regular trimming or filing by a podiatrist reduces fungal load and speeds topical drug absorption.
• Laser therapy – Nd:YAG lasers claim to heat and destroy fungal cells; evidence is mixed, and insurance coverage is limited.
• Surgical nail removal – indicated for severely infected or painful nails, or when rapid resolution is needed before reconstructive foot surgery.

4. Lifestyle and adjunct measures

• Keep feet clean and dry; change socks at least once daily.
• Use antifungal powder or spray in shoes.
• Avoid tight footwear; wear breathable materials.
• Disinfect pedicure tools or use disposable kits.

Living with Fungal Toenail Infection (Onychomycosis)

Daily management tips

• Foot hygiene – wash feet with mild soap, dry thoroughly (especially between toes) after showering.
• Socks & footwear – wear moisture‑wicking socks (cotton or wool blends) and change them if feet become sweaty.
• Footwear rotation – alternate shoes every day to allow them to air out.
• Nail care – trim nails straight across, file edges, and keep length short to reduce trauma.
• Antifungal prophylaxis – occasional use of over‑the‑counter topical antifungal sprays can keep tinea pedis at bay, reducing the source of infection.
• Monitor progress – take monthly photos of the affected nail to track improvement; report any worsening to your clinician.

Prevention

Because onychomycosis thrives in moist, warm environments, prevention focuses on reducing exposure and maintaining nail health.

• Wear flip‑flops or shower shoes in public pools, gyms, and locker rooms.
• Avoid walking barefoot on damp floors.
• Choose breathable footwear; consider shoes made of leather or mesh.
• Keep toenails trimmed and filed; avoid aggressive cutting that creates micro‑trauma.
• Limit the use of nail polish and artificial nails – they trap moisture.
• Treat athlete's foot promptly; a fungal toe infection often follows tinea pedis.
• For diabetics, schedule regular foot examinations with a podiatrist.

Complications

If left untreated, onychomycosis can lead to several problems:

• Secondary bacterial infection – cracked nail beds may become portals for Staphylococcus or Streptococcus, causing cellulitis.
• Pain and functional limitation – thickened nails can impede walking and cause pressure ulcers under the nail.
• Spread to other nails or skin – infection may disseminate to adjacent toes, fingernails, or cause widespread tinea pedis.
• Complications in diabetes – poor circulation and neuropathy heighten the risk of foot ulcers, leading to possible amputation.
• Psychosocial impact – visible nail changes can affect self‑esteem and cause social embarrassment.

When to Seek Emergency Care

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Sources: Mayo Clinic. “Onychomycosis (fungal nail infection).” 2023; CDC. “Fungal Diseases – Onychomycosis.” 2022; NIH National Library of Medicine. “Management of Onychomycosis.” 2021; WHO. “Global burden of fungal disease.” 2022; Cleveland Clinic. “Nail Fungus Treatment Options.” 2023.

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