Infections - Fungal
Toenail Fungus (Onychomycosis)
WHAT IS IT
A fungal infection of the nail
HOW COMMON
Very common, more so with age
CONTAGIOUS?
Yes — via damp floors, shoes, and clippers
CURABLE?
Treatable, but slow; nails grow out over months
What Is It?
Onychomycosis is a fungal infection of the nails — usually the toenails — that makes them thick, discolored (yellow, white, or brown), brittle, and sometimes lifted from the nail bed. It's often linked to athlete's foot. Treatment works slowly because the nail must grow out; toenails can take 12–18 months to look normal.
Signs & Symptoms
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Thick, brittle, or crumbling nails
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Yellow, white, or brown discoloration
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Nail lifting away from the nail bed
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Debris building up under the nail
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Often alongside athlete's foot
Why Does It Happen?
It's caused by the same fungi that cause athlete's foot, which get into the nail through small cracks or from nearby skin infection. Warm, damp shoes, communal showers, nail trauma, older age, diabetes, and poor circulation all raise the risk. It can spread between nails and to other people. Confirming the diagnosis before treatment is important.
Treatment Options
Because treatment is long and can affect the liver (oral options), it's best to confirm the fungus first. Treatment is optional if the nail isn't bothering you.
CONFIRM FIRST
A nail sample confirms fungus before starting lengthy treatment.
ORAL ANTIFUNGALS
Terbinafine is first-line and most effective; needs weeks of pills.
TOPICAL ANTIFUNGALS
Efinaconazole or similar for milder cases or when pills aren't suitable.
PREVENT RECURRENCE
Treat athlete's foot and use antifungal foot care long-term.
Tips for Managing It at Home
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Keep nails trimmed short and filed down
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Don't share nail clippers; disinfect tools between uses
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Treat athlete's foot and keep feet dry; rotate/replace old shoes
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Be patient — a clear toenail can take 12–18 months to grow out
When to Call Your Provider
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You have diabetes or poor circulation and notice nail changes
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The toe becomes painful, red, or swollen (possible infection)
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Treatment isn't helping after growing out the nail
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You're unsure whether it's fungus or another nail problem
Sources & further reading
The information in this handout is based on general dermatology guidance from the reputable organizations below. These links are provided for patients who wish to read more from trusted sources.
American Academy of Dermatology (AAD). Nail Fungus. https://www.aad.org/public/diseases/a-z/nail-fungus
Canadian Dermatology Association (CDA). Nail Fungus and Infection. https://dermatology.ca/public-patients/diseases-conditions/nail-conditions/nail-fungus-and-infection/
DermNet. Onychomycosis (Fungal Nail Infection). https://dermnetnz.org/topics/onychomycosis
MSD/Merck Manual. Onychomycosis. https://www.msdmanuals.com/professional/dermatologic-disorders/nail-disorders/onychomycosis
This handout is for general education and does not replace advice from your own provider. Always follow your provider’s specific instructions.
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