Onychomycosis

Key facts

• Onychomycosis is a fungal infection of the fingernails or toenails, far more common in toenails.
• Affected nails typically turn yellow, white or brown, thicken, and may crumble at the edges; the condition progresses slowly if untreated.
• Dermatophyte fungi cause most cases, and prior athlete's foot (tinea pedis) frequently spreads upward to the nails.
• Oral antifungals, terbinafine first-line or griseofulvin as an alternative, treat the infection over several months because the drug must penetrate the nail as it grows out.

What onychomycosis looks like

Onychomycosis is a fungal infection of the fingernails or toenails. Affected nails typically turn yellow, white or brown, thicken and may crumble at the edges. Toenails are far more commonly affected than fingernails, and the condition tends to progress slowly if left untreated, sometimes over years.

Who is more susceptible

Warm, humid conditions and prolonged closed footwear favour the dermatophyte fungi that cause most cases, as do communal bathing areas and swimming pools. People with diabetes or reduced circulation in the feet are more susceptible, and prior athlete's foot (tinea pedis) frequently spreads upward to the nails.

How onychomycosis is treated

Because nails grow slowly and form a physical barrier, oral antifungals penetrate more reliably than topical treatments alone. Terbinafine is the most widely used first-line agent; it accumulates in nail tissue and keeps working after the course ends. Griseofulvin is an older alternative suited to certain fungal species. Both are antifungals. Treatment courses typically run several months, reflecting how long a nail takes to grow out rather than how strong the drug is.

When to see a doctor

If a nail becomes painful, develops an odour, or shows signs of infection spreading into the surrounding skin, a clinician should assess it promptly; diagnosis is often confirmed with a nail clipping before treatment starts.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.