Nail Fungus (Onychomycosis)

What causes nail fungus

• Dermatophytes, mainly Trichophyton rubrum, cause most toenail infections. They often spread from athlete's foot.
• Yeasts (Candida) more often affect fingernails, especially in people whose hands are often wet.
• Non-dermatophyte molds cause a smaller share and are harder to treat.

Risk factors:

• older age (nails grow slower and circulation declines)
• athlete's foot
• sweaty feet and tight, closed shoes
• walking barefoot in gyms, pools and showers
• diabetes, poor circulation, weakened immunity
• nail injury or nail psoriasis
• smoking
• family history

Symptoms

• white, yellow, brown or greenish discoloration
• thickened nail that is hard to trim
• brittle, crumbly or ragged edges
• debris building up under the nail
• the nail separating from the nail bed (onycholysis)
• distorted shape
• discomfort in shoes or when walking
• sometimes a faint unpleasant smell

Types

Conditions that look like nail fungus

Only about half of abnormal-looking nails are actually fungal. Look-alikes include:

• nail psoriasis: pitting, oil-drop discoloration, lifting
• nail trauma: from running, tight shoes or injury
• lichen planus and eczema
• age-related nail thickening
• green nail syndrome from Pseudomonas bacteria
• subungual melanoma: a dark band or patch, which needs urgent evaluation

That is why dermatologists recommend confirming the diagnosis before starting oral treatment.

Diagnosis

A doctor or podiatrist trims the nail and scrapes debris from under it for:

• KOH microscopy to see fungal elements
• fungal culture to identify the species
• PCR testing, which is faster and more sensitive
• nail histology (PAS stain) of clippings

Treatment

Oral medicines (most effective)

• Terbinafine: taken daily for about 12 weeks for toenails (6 weeks for fingernails). Complete cure rates are around 40 to 50%, and clinical improvement is higher. A baseline liver test may be checked. It is not used in liver disease.
• Itraconazole: daily or pulse dosing; more drug interactions and not suitable with heart failure.
• Fluconazole: sometimes used off-label.

The nail will still look abnormal at the end of treatment. A healthy nail grows out from the base over months.

Topical treatments

• Efinaconazole and tavaborole solutions: applied daily for 48 weeks; lower cure rates, but useful for mild to moderate infection without involvement of the nail base, or when oral medicines are unsuitable.
• Ciclopirox nail lacquer: modest effectiveness.
• Over-the-counter creams treat athlete's foot but do not penetrate the nail well.

Other approaches

• Debridement: regular trimming and thinning of the nail by a podiatrist reduces pain and helps topical treatment penetrate.
• Nail removal: surgical or chemical, for painful or resistant nails, usually combined with antifungals.
• Laser therapy: some improvement reported, but evidence is limited and costs are high.

Home remedies such as tea tree oil, vinegar soaks or menthol rubs have little evidence of cure.

Preventing nail fungus and recurrence

Recurrence happens in up to a quarter or more of people.

• Treat athlete's foot promptly.
• Keep feet clean and dry; change socks daily.
• Wear breathable shoes and rotate pairs.
• Wear sandals in communal showers and pools.
• Trim nails straight across; do not share clippers.
• Apply antifungal powder or spray in shoes.
• Consider periodic topical antifungal use after cure if you are prone to recurrence.

Frequently asked questions

What causes toenail fungus?

Toenail fungus is mostly caused by dermatophyte fungi, the same ones that cause athlete's foot. They thrive in warm, moist environments like sweaty shoes and communal showers. Older age, diabetes, poor circulation, nail injury and athlete's foot raise the risk.

What is the fastest way to get rid of nail fungus?

Oral terbinafine is the most effective treatment, usually for 12 weeks for toenails. Even so, the nail must grow out, which takes 12 to 18 months. Topical prescription solutions work more slowly and are best for mild cases.

Can nail fungus go away on its own?

Rarely. Nail fungus usually persists or slowly spreads without treatment. Some people choose not to treat mild, painless infections, but treatment is advised for people with diabetes, pain or spreading infection.

Is nail fungus contagious?

Yes, mildly. The fungi can spread from nail to nail, to the skin as athlete's foot, and to other people through shared floors, towels, shoes or nail tools. Keeping feet dry and not sharing items reduces spread.

How do I know if it is nail fungus or something else?

Many conditions look like nail fungus, including psoriasis, injury and age-related changes. A doctor can confirm a fungal infection by testing nail clippings. Testing is recommended before taking oral antifungal medicines.