Fungal Nail Infection
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Fungal Nail Infection: Causes, Treatment and Timescales
Why treatment takes months rather than weeks, how to tell an infected nail from the several things that mimic one, and what actually stops it coming back.
Key fact: Treatment is slow because nails are slow. A toenail grows about 1mm a month and takes 12 to 18 months to replace itself entirely, so a nail can be free of fungus months before it looks normal. Judging treatment by appearance at three months is judging it far too early.
What a fungal nail infection is
Onychomycosis is a fungal infection of the nail plate and the nail bed beneath it. Most cases are caused by dermatophytes — the same group of fungi responsible for athlete's foot and ringworm — and most start in a toenail rather than a fingernail.
It is not a hygiene problem and it is not trivial. Left alone it tends to spread, first through the rest of that nail, then to neighbouring nails, and it does not resolve on its own.
What it looks like
- Discolouration — white, yellow, brown or occasionally green streaks or patches, usually starting at the free edge or the side
- Thickening, so the nail becomes hard to cut and uncomfortable in shoes
- Crumbling or brittleness, with debris building up underneath
- Distortion of shape, and in advanced cases separation of the nail from the bed
- Usually painless, at least early on — pain generally comes from pressure in footwear
- Often alongside athlete's foot, with itchy, scaly or cracked skin between the toes
Why it happens
Warm, damp feet
Shoes worn all day, sweaty socks, and communal showers or pools. Fungi thrive in exactly those conditions.
Untreated athlete's foot
The commonest source. Fungus on the skin spreads into the nail, and an untreated foot keeps reinfecting it.
Nail damage
Repeated trauma from running or tight shoes creates a way in, which is why the big toenail is so often first.
Age
Nails grow more slowly and become more brittle, and infection becomes considerably more common with each decade.
Diabetes and circulation problems
Both raise the risk and make complications more likely, which is why foot care matters more in these groups.
A weakened immune system
From illness or medication, making infection easier to acquire and harder to clear.
It is not always fungal
Fungal infection accounts for roughly half of all nail disease — which means about half of abnormal nails are something else. Psoriasis, repeated trauma from footwear, lichen planus and, rarely, a melanoma of the nail can all produce a nail that looks convincingly infected. Is it really a fungal nail? covers how they differ.
Get a new dark streak in a nail assessed promptly. A brown or black band running lengthwise down a nail — particularly a single nail, wider than about 3mm, with an irregular edge, widening over time, or with pigment spreading onto the surrounding skin — needs a proper look rather than antifungal treatment. Subungual melanoma is uncommon but is repeatedly mistaken for a fungal nail or an old bruise.
Confirming it
Nail clippings and subungual debris can be sent to a laboratory for microscopy and culture. This matters most before starting oral antifungal treatment, for two reasons: half of abnormal nails are not fungal, and tablets carry more significant risks than a lacquer does.
- Samples are taken before treatment starts — antifungal treatment already begun makes the result unreliable
- Culture takes several weeks, which is normal rather than a delay in the system
- A negative result does not always exclude infection, and sampling is sometimes repeated
- Local practice varies on when samples are required, and some areas restrict testing to specific situations
Treatment
| Approach | Suits | Typical course |
|---|---|---|
| Antifungal nail lacquer — amorolfine 5%, sold as amorolfine, Curanail and Loceryl | Early, superficial or distal infection affecting only one or two nails, without involvement of the growing base | Applied once or twice weekly after filing — 6 months for fingernails, 9 to 12 months for toenails |
| Antifungal tablets — terbinafine 250mg | More extensive infection, several nails, involvement of the nail base, or failed topical treatment | Around 6 weeks to 3 months for fingernails, 3 to 6 months for toenails |
| Antifungal cream — terbinafine 1% cream | The athlete's foot alongside it — not the nail itself | Usually 1 to 2 weeks for skin |
| Nail softening and removal kits — such as Scholl fungal nail treatment | Reducing thickened nail and treating the exposed surface | Used over weeks, often alongside other treatment |
Fungal nail treatments compared sets out which is appropriate when, and what monitoring tablets involve.
How long it takes
The practical consequence: the sign that treatment is working is healthy nail growing from the base, not the damaged part looking better. The damaged part never recovers; it grows out and is replaced. Expecting an improvement in appearance within weeks is the commonest reason people stop treatment before it has had a chance.
How well treatment works
Honestly, moderately. Roughly half of treated nails end up looking fully normal. In a further two in ten the fungus is cleared but the nail never looks quite right again, usually because of damage that predated or accompanied the infection. Around one in four cleared infections comes back within three years.
Topical lacquer alone has lower cure rates than tablets, which is why it is reserved for early, limited infection rather than used as a first attempt at everything.
Stopping it coming back
- Treat the athlete's foot, and keep treating it — the skin is the reservoir that reinfects the nail. See athlete's foot and reinfection
- Dry between the toes properly after washing
- Rotate shoes so each pair dries out fully, and consider replacing shoes worn throughout an infection
- Change socks daily and wash them hot
- Wear flip-flops in communal showers, changing rooms and around pools
- Keep nails short and cut straight across, and do not share clippers
- Do not use the same clippers on infected and healthy nails
When to get it looked at
Do not self-treat — get assessed — if: you have diabetes, poor circulation or a weakened immune system; the nail is painful, or the surrounding skin is red, swollen or discharging; a new dark streak has appeared in a nail; the nail is separating from the bed; several nails are involved; or treatment bought from a pharmacy has not worked. Seek urgent advice for a spreading red, hot, painful area on the foot, which can indicate cellulitis — a particular risk where the skin between the toes is cracked.
Frequently Asked Questions
How long does it take to cure a fungal nail infection?
Months. Lacquer is used for 6 months on fingernails and 9 to 12 months on toenails; tablets are usually taken for 6 weeks to 3 months for fingernails and 3 to 6 months for toenails. Because a toenail takes 12 to 18 months to grow out completely, the nail can be clear of fungus long before it looks normal.
Will a fungal nail go away on its own?
No. Untreated it tends to spread through the rest of the nail and then to neighbouring nails. It also acts as a reservoir that keeps reinfecting the skin, so athlete's foot keeps returning too.
Do I need tablets or is nail paint enough?
Lacquer is appropriate for early, superficial or distal infection affecting only one or two nails, without involvement of the growing base at the bottom of the nail. More extensive infection, several nails, or infection reaching the nail base usually needs oral treatment, because lacquer does not penetrate far enough.
Is a thick discoloured nail always fungal?
No. Fungal infection accounts for roughly half of all nail disease, so about half of abnormal nails are something else, including psoriasis, repeated trauma from footwear, and lichen planus. This is why laboratory confirmation on nail clippings is recommended before starting oral antifungal tablets.
When should I worry about a dark line in my nail?
Get it assessed promptly if a brown or black band runs lengthwise down a nail, particularly a single nail, if it is wider than about 3mm, has an irregular edge, is widening, or the pigment extends onto the surrounding skin. Subungual melanoma is uncommon but is often mistaken for a fungal nail or a bruise.
Why does it keep coming back?
Usually because the athlete's foot was never fully treated, or because shoes worn throughout the infection were kept. Around one in four cleared infections returns within three years, and reinfection from the skin is the commonest route.
References
- NHS. Fungal nail infection. nhs.uk
- NHS. Athlete's foot. nhs.uk
- National Institute for Health and Care Excellence. Clinical Knowledge Summary: Fungal nail infection. cks.nice.org.uk
- DermNet. Fungal nail infections. dermnetnz.org
- National Institute for Health and Care Excellence. Suspected cancer: recognition and referral (NG12). nice.org.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. An abnormal nail is not always a fungal infection, and a new dark streak in a nail should always be assessed. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.
