- Fungal nail infection (onychomycosis) causes nails to become thick, discolored (yellow, brown, white), and crumbly.
- It is caused by the same fungi that cause athlete's foot, and the two conditions often occur together.
- Treatment options range from in-office nail debridement and topical antifungals to oral antifungal medications for severe cases.
- Treatment success depends on consistency and patience — toenails grow slowly, so visible improvement takes 6–12 months.
- Untreated fungal nails can become thick enough to cause pain, ingrown nails, and (in diabetics) serve as entry points for serious infection.
What is a fungal nail infection?
A fungal nail infection — clinically called onychomycosis — is a fungal infection that invades the toenail or the nail bed beneath it. It is one of the most common nail conditions, affecting an estimated 14% of adults and a significantly higher percentage of older adults. Infections typically start at the edge or tip of the nail and gradually spread underneath, causing the nail to become thick, discolored, crumbly, and sometimes painful.
The fungi responsible are usually the same dermatophytes that cause athlete's foot (Trichophyton rubrum is the most common), and the two conditions frequently coexist. Once established, fungal nail infections are stubborn — the nail plate is hard for topical medications to penetrate, and the slow growth of toenails means treatment courses are long. Risk factors include sweaty feet, walking barefoot in public locker rooms or pools, prior nail trauma, diabetes, peripheral vascular disease, and any condition that impairs immune function.
At Northwest Extremity Specialists, our board-certified podiatrists offer a stepped approach to fungal nails across all 8 clinics. Mild cases respond to in-office nail debridement combined with prescription topical antifungals. Moderate to severe cases benefit from oral antifungal medications, which have much higher cure rates but require liver function monitoring. Patience matters: even successful treatment takes 6–12 months to show visible improvement because that is how long it takes for a healthy nail to grow out.
What it feels like
Fungal nail infections develop gradually and have a recognizable look:
- Thickening of the nail
- Yellow, brown, white, or black discoloration
- Crumbling or brittle nail edges
- A distorted or misshapen nail
- Foul odor from under the nail
- Separation of the nail from the nail bed
- Pain in the toe, especially with shoes
- Often coexists with athlete's foot (scaly, itchy skin between toes or on the soles)
Why it develops
Fungal nail infections develop when fungi enter the nail or surrounding skin. Common contributors:
- Untreated athlete's foot that spreads to the nails
- Walking barefoot in locker rooms, pools, or showers
- Sweaty feet that create a warm, moist environment for fungal growth
- Prior nail trauma that allowed fungi to enter
- Diabetes or peripheral vascular disease
- Older age (nails grow more slowly and are more easily invaded)
- Immunosuppression
- Family history of fungal nails
How we diagnose a fungal nail infection
Fungal nails are often recognizable on visual inspection, but appearance alone can be misleading — other nail conditions (psoriasis, trauma, lichen planus) can look similar. Your provider may take a small sample of the affected nail for laboratory testing (KOH prep, fungal culture, or PCR) to confirm the diagnosis before starting long-term treatment. This is particularly important if oral antifungal therapy is being considered, given the cost and need for liver monitoring. Most patients leave the same day with a plan and (when appropriate) samples submitted for confirmation.
Non-surgical care
Treatment is matched to the severity of infection and the patient's overall health. Most patients are managed with a combination of approaches:
- Regular in-office nail debridement to reduce thickness and improve topical penetration
- Prescription topical antifungals (efinaconazole, tavaborole, ciclopirox) for mild-to-moderate cases
- Oral antifungal medications (terbinafine, itraconazole) for moderate-to-severe cases — much higher cure rates but require liver function monitoring
- Treatment of any coexisting athlete's foot to prevent re-infection
- Footwear and sock recommendations to reduce humidity (breathable shoes, moisture-wicking socks)
- Antifungal powders or sprays in shoes
- For diabetic patients, more aggressive treatment and closer monitoring
- Permanent nail removal (matrixectomy) in selected cases with chronic ingrown fungal nails
When to see a specialist
- Thick or discolored toenails that have been getting worse over months
- Pain or pressure from a thickened nail
- Fungal nail infection in a diabetic patient — earlier treatment matters
- Multiple nails affected
- A nail that's separating from the nail bed
- Cosmetic concern — treatment can dramatically improve appearance over time
Fungal nail care is offered at all 8 of our clinics by any of our board-certified podiatrists. Diabetic patients are typically managed by Dr. Cara Beach at our Cedar Mill and Hoyt offices as part of their broader diabetic foot care program.