Condition

Nail Fungus (Onychomycosis)

Nail fungus is a fungal infection inside the nail. It makes the nail thick, crumbly and discoloured, usually on the big toe. It is common and harmless, but slow and stubborn to treat.
At a Glance

Nail fungus is a fungal infection living inside the nail, making it thick, crumbly and yellow, white or brown. Two things are worth knowing before you start treating it: roughly half of thickened, discoloured nails turn out not to be fungus at all, so a nail clipping sent to the lab is worth doing first; and even when treatment works, the nail takes twelve to eighteen months to grow out, so it still looks bad long after the fungus is dead. Antifungal nail lacquers cure only a small share of cases and much less on a thick or fully involved nail. Terbinafine tablets are considerably more effective and need liver blood tests — which is exactly why confirming the diagnosis first is worth the extra visit.

Key Facts

How CommonVery common. Around 10 percent of adults, rising to roughly half of people over 70.
Who Gets ItMore common with age, in men, and in people with athlete's foot, diabetes, poor circulation, psoriasis or a weakened immune system. Also anyone whose feet are in closed shoes all day.
Chronic or CurableCurable, but slowly and not reliably. Even the best treatment does not work for everyone, and it comes back in roughly one in five people.
Rx RequiredFor anything more than a small patch on the tip of one nail, yes. Over-the-counter products very rarely cure it.
ContagiousMildly. It spreads through shared floors, shared nail clippers, shared shoes, and from your own athlete's foot.
CostWorth asking about. Generic terbinafine tablets are cheap. Prescription nail lacquers are often expensive and not always covered, and laser treatment is usually not covered at all.

Symptoms

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Nail fungus usually starts at the free edge or the side of one nail and works its way back toward the base. It rarely hurts, which is why people live with it for years.

What it looks and feels like

Yellow, white, brown or grey discolouration — often starting as a streak or wedge at the tip or edge.
Thickening — the nail gets harder to cut and can lift away from the nail bed.
Crumbly, chalky debris — build-up under the nail that flakes out when you clip it.
Ridges and an uneven surface — the nail loses its smooth shine.
A separated nail — a hollow, sometimes dark space between the nail and the skin beneath.
Usually one or two nails at first — rarely all of them at once, and rarely symmetrical. If every nail on both hands and feet changed at the same time, think of something else.
Little or no pain — until the nail is thick enough to press against a shoe.
Sometimes a smell, particularly with a lot of debris under the nail.

Where it shows up

  • Toenails, and the big toe most of all — by far the most common.
  • Fingernails — much less common. Fungal fingernail infection nearly always occurs alongside a toenail infection, so a single changed fingernail with normal toenails should raise a question.
  • On skin nearby — athlete's foot on the sole or between the toes is present in most people with toenail fungus, and it is usually where the nail infection came from.

How it looks on different skin tones

The nail changes themselves look the same on all skin tones. What differs is the surrounding context: on brown and Black skin it is normal to have brown or black pigmented streaks running the length of one or more nails, which is a harmless pattern called melanonychia and has nothing to do with fungus. It becomes worth checking when a single band is new, is getting wider, is very dark or irregular, or when the pigment extends onto the skin at the base of the nail. That is a different question from fungus and it is answered by a dermatologist looking, not by antifungal treatment.

Light
Medium
Brown
Deep

Plenty of thick, discoloured nails are not fungal. If yours does not fit the description above, see Lookalikes near the bottom of this page.

Causes & Risk Factors

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Nail fungus is usually caused by the same dermatophyte fungi that cause athlete's foot, and Trichophyton rubrum is the usual culprit. Yeasts and moulds cause a minority of cases, mostly in fingernails and in people with damaged nails or a weakened immune system, and they respond to different drugs — one of the reasons identifying what is actually growing is useful.

The fungus gets in through a small gap: a separation between the nail and the nail bed, a crack, or damage from a knock, tight shoes or repeated pressure. From there it grows into the nail plate, which is dead tissue with no blood supply. That last detail explains most of what is frustrating about this condition. There is no blood flow into a nail, so the immune system cannot reach the infection and creams cannot get through the hard nail surface easily either. The main risk factors are age, because nails grow more slowly and get more damaged over a lifetime; untreated athlete's foot, which is the reservoir the nail infection comes from and returns to; diabetes and poor circulation; and anything that damages nails, including sport, closed shoes and nail salon instruments that are not properly sterilised. Nail polish and gel manicures do not cause fungal infection, but they hide it, so it is often further along by the time it is spotted.

What Hurts and What Helps

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What Makes It Worse

  • Leaving athlete's foot untreated. The skin and the nails reinfect each other, and treating the nail alone tends to fail.
  • Wearing tight shoes that press on the nail, and shoes that are damp inside.
  • Walking barefoot on communal wet floors — gyms, pools, changing rooms.
  • Shared nail clippers and files, at home or in a salon that does not sterilise properly.
  • Picking or over-trimming the nail so it separates from the nail bed, which gives the fungus more room.
  • Covering it with nail polish or gel. It hides the problem, and gel removal damages the nail surface further.
  • Expecting a topical to clear a nail that is thick or fully involved. It will not, and years get lost this way.

Daily Habits That Help

  • Getting the diagnosis confirmed before starting. A nail clipping sent for testing takes one visit and saves a year of treating the wrong thing.
  • Treating the athlete's foot on the skin at the same time, every time.
  • Keeping nails cut short and filing the surface thin. This removes fungus-loaded nail, relieves pressure, and lets a topical reach further in.
  • Softening a very thick nail with a urea cream so more of it can be filed away.
  • Using an antifungal powder or spray in your shoes so you are not reinfecting yourself daily.
  • Drying between the toes properly, and rotating shoes so each pair dries out.
+2 more
  • Being realistic about time. Toenails grow about 1 to 2 millimetres a month. Twelve to eighteen months for a big toenail to fully replace itself is normal, and nothing speeds that up.
  • Judging progress by the new growth at the base of the nail, not by the old damaged part at the tip.

Try at Home

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Be realistic about this band. Over-the-counter products can help a small patch on the tip of one nail and can keep the fungus from spreading, but they do not cure a thick or fully involved nail. The most useful things here are trimming, filing and keeping your shoes and skin clear.

Keeping the nail cut short and filed thin
Always
Cutting the nail back and filing the surface down removes a large amount of the fungus, takes the pressure off the toe, and lets any topical treatment reach further in. It does more than most people expect, and it costs nothing.
Treating the skin and the shoes at the same time
Always
Most people with nail fungus also have athlete's foot, and the two reinfect each other. Treating the nail while leaving the skin and the shoe lining alone is the most common reason a year of treatment fails. Antifungal cream on the skin, powder in the shoes, and rotate two pairs.
Moderate evidence
Softens a thick nail so more of it can be filed or clipped away, and helps other treatments get through. It does not kill fungus — it makes the treatments that do more likely to reach it.
Limited evidence
Terbinafine or clotrimazole cream clears the athlete's foot on the skin around the nail, which is where the reinfection comes from. Be clear about what it does and does not do: it will not cure the nail itself, because it cannot get through the nail plate.
Limited evidence
One of the over-the-counter nail solutions sold for this. It has some antifungal activity, but there is very little evidence it cures nail infection, and none suggesting it works on a thick or fully involved nail. Reasonable for a small patch on the tip; not a substitute for prescription treatment.
Limited evidence
People ask about this constantly, so here is the honest position. One small study found some improvement in a handful of people, with no comparison group. It is cheap and harmless, so trying it on a mild nail is reasonable. It is nowhere near as effective as a prescription, and it is not a reason to delay getting a real treatment for a nail that bothers you.
Limited evidence
Studied in nail infection with modest results — some improvement in appearance, but poor rates of actually clearing the fungus. It can also cause an allergic rash. Worth knowing about, not worth relying on for a nail you want cured.

When to See a Dermatologist

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This is one of the conditions where seeing a dermatologist first is genuinely worth it, rather than something to try after a year of drugstore products. Book a visit if:

  • You are thinking about treating it at all. Confirming that it is fungus before starting is the single most useful step, and it is a nail clipping rather than anything invasive.
  • More than one nail is affected, or more than half of any nail.
  • The nail is thick, lifting, or painful in shoes.
  • You have diabetes, poor circulation or a weakened immune system. Nail problems carry more risk in those situations and should not be self-treated.
  • A single nail has a new dark brown or black band running along its length, especially if it is widening, irregular, or the colour extends onto the skin at the base of the nail. This is not fungus, and it is worth looking at.
  • Treatment has been used properly for a year and there is no clear new healthy growth at the base.

What the visit gets you: a definite answer on whether this is fungus, and if so which type, which decides whether terbinafine or a different drug is the right one. You also get a realistic conversation about what each option can and cannot achieve, and whether treating it at all is worth it for you — which is a legitimate conclusion for a symptom-free nail.

What Happens at the Dermatologist?+

This is the condition where testing matters most, and it is the reason to go in before starting treatment rather than after. Around half of thickened, discoloured nails sent for testing turn out not to be fungal at all. Treating those with antifungal tablets means a year of pointless medication, blood tests and cost, while whatever is actually wrong goes untreated.

Nail clipping with PAS stain. A piece of the affected nail is clipped off, along with some of the debris underneath, and sent to a lab where it is stained to show fungus inside the nail. It does not hurt at all. It is the most sensitive of the common tests, results come back in days, and it answers the only question that matters at this point: is there fungus in this nail or not? This is the test that changes management, and it should be done before anyone starts oral terbinafine.

Fungal culture. The same material is grown on a plate, which takes two to four weeks. It is less sensitive than PAS staining and often comes back negative even in real infections, so a negative culture alone does not rule fungus out. What it adds is the name of the organism, and that does change treatment: dermatophytes respond well to terbinafine, whereas some yeasts and moulds do not and need itraconazole or a different approach.

PCR. A molecular test that detects fungal DNA in the nail. It is the fastest, often within a few days, and it both confirms infection and names the organism. It costs more and is not available everywhere, but where it is, it does the job of both tests above in one step.

Dermoscopy. A magnifier used in the room. It does not confirm fungus, but it helps separate fungal patterns from nail psoriasis and from trauma, and it is the tool used to assess a pigmented band in a nail.

Blood tests are not used to diagnose nail fungus. They are used before and during oral terbinafine or itraconazole to check liver function. That monitoring is a reasonable trade for a treatment that works — it is a poor trade for treating a nail that never had fungus in it.

Prescription Treatments

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The treatments that actually clear nail fungus. Lacquers suit a mild nail or someone who cannot take tablets; tablets are considerably more effective and are the usual choice when more than the tip of the nail is involved.

Topical prescriptions
Moderate evidence
The most effective of the prescription nail solutions. Applied daily for 48 weeks. Even so, complete cure is achieved in only around one in six people, and considerably less on a thick or fully involved nail. It suits a mild infection, or someone who cannot take tablets. It is often expensive and not always covered.
Topical prescriptions
Moderate evidence
Another daily nail solution used for 48 weeks. It gets into the nail well, but complete cure rates are lower still — under one in ten in the trials. Same role as efinaconazole: mild infection, or when tablets are not an option.
Topical prescriptions
Limited evidence
The oldest of the nail lacquers and usually the cheapest. It is also the least effective, with complete cure in well under one in ten, and it has to be painted on daily for 48 weeks with the build-up wiped off weekly with alcohol. A lot of effort for a low chance.
Pills and injections
Strong evidence
The most effective treatment there is, and the usual choice when more than the tip of the nail is involved. Twelve weeks for toenails, six for fingernails. Complete cure is achieved in roughly four to five out of ten people, which is far better than any topical but is not a guarantee. Liver blood tests are checked before starting, which is exactly why confirming the diagnosis first is worth doing.
Pills and injections
Strong evidence
The alternative pill, often given as one week on and three weeks off, repeated three times. It is the better choice when the culture shows a yeast or mould rather than a dermatophyte, since terbinafine does not cover those well. It interacts with a long list of medicines and is avoided in heart failure.
Pills and injections
Limited evidence
Taken once a week for six to twelve months. It is used off-label and is the least effective of the three pills for nails, so it is generally a third choice when terbinafine and itraconazole are not suitable.

In-Office Treatments

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Done in a clinic. One of these is genuinely useful, one is comfort rather than cure, and one is expensive and oversold — the descriptions say which is which.

Moderate evidence
A podiatrist or dermatologist thins and cuts back the thickened nail with a burr. It relieves pressure and pain straight away, removes a lot of infected nail, and meaningfully improves how well a topical works. It does not cure anything on its own, but it is the most useful in-office option here and it is usually covered.
Limited evidence
Marketed heavily, and worth being sceptical about. Laser devices are approved only for a temporary increase in clear nail, which is a deliberately modest claim and not the same as curing anything. Cure rates in independent studies are well below tablets, courses run several hundred to a few thousand dollars, and it is rarely covered by insurance. It is an option if you cannot take tablets and understand what you are buying.
Limited evidence
The nail is removed, either surgically under local anaesthetic or chemically with a urea paste. It is used when a nail is painful or so thick that nothing can reach the infection, not as a cure — the new nail grows back infected unless antifungal treatment is used alongside it. The replacement nail takes twelve to eighteen months to regrow and may be permanently misshapen.

What to Expect

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Step 1
Nothing visible for the first three months

This is normal and it is not a sign of failure. The damaged part of the nail cannot repair itself. All you can look for is a band of clear, healthy nail appearing at the base.

Step 2
Months three to six

A clear strip should be visible at the base of the nail and slowly pushing the damaged part forward. This is the only real measure of whether treatment is working.

Step 3
Twelve to eighteen months for a big toenail

Toenails grow roughly 1 to 2 millimetres a month, and a big toenail replaces itself completely in about a year to eighteen months. Fingernails take about half that. The fungus can be dead for a year and the nail will still look bad until the damaged part has grown off the end.

Step 4
The nail may never look completely normal

If the nail bed was damaged before or during the infection, some ridging, thickening or discolouration can be permanent. That is worth knowing before you start, not after.

Step 5
It comes back in about one in five people

Usually because the athlete's foot on the skin was never treated, or because the shoes were never dealt with. Ongoing prevention is part of the plan, not an optional extra.

Step 6
If there is no new clear growth after a year

Stop and reassess rather than continuing. Either it is not fungus, or it is an organism the drug does not cover, or the nail is too damaged for treatment to work.

Complications

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For most people nail fungus is a cosmetic and comfort problem rather than a health one, and choosing not to treat a painless nail is a reasonable decision. A few things do follow if it is left.

Pain and pressure
A thickened nail presses against the top of a shoe, and can dig into the nail fold and cause an ingrown nail.
Permanent nail damage
Long-standing infection can scar the nail bed so the nail never grows back smooth, even after successful treatment.
Spread
To the other nails, to the skin of the feet, and to other people through shared floors, clippers and shoes.
A reservoir for athlete's foot
Infected nails keep reinfecting the skin, which is why skin treatment appears to keep failing.
Cellulitis, mainly in people with diabetes or poor circulation
Cracks in thickened nails and the skin around them let bacteria in, and in a foot with reduced sensation or blood flow that is a more serious problem. This is the group for whom treating nail fungus is a genuine medical priority rather than a cosmetic one.
Side effects of treatment
Terbinafine can affect the liver, and can alter taste or smell, occasionally permanently. Itraconazole interacts with a long list of medicines. These are uncommon but real, and they are the reason to be sure of the diagnosis before starting.

Lookalikes

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Around half of thick, discoloured nails are not fungal. These are what they usually turn out to be, and it is why a nail clipping is worth doing before a year of treatment.

  • Nail psoriasis — the most common mimic. Look for small pinprick pits in the nail surface, an oil-drop patch of orange-brown discolouration under the nail, and separation of the nail with a red-brown border. It often affects several nails, including fingernails, and usually comes with psoriasis somewhere on the skin or scalp. Antifungal treatment does nothing for it.
  • Trauma — repeated knocks from running, tight shoes or a single injury thicken and discolour a nail in a way that looks identical to fungus. The clue is usually one nail on the foot that takes the most impact, and no athlete's foot on the skin.
  • Subungual melanoma — uncommon, but it should be named. This is a skin cancer under the nail, and it looks like a brown or black band running the length of a single nail. Features that make it worth checking are a band that is new in an adult, getting wider, dark or irregular in colour, on the thumb or big toe, or where the pigment extends onto the skin of the nail fold. On brown and Black skin, harmless pigmented bands are common and usually affect several nails, so context matters. This is not a reason to panic about a yellow crumbly nail, which looks nothing like it — but a new dark band in one nail is worth showing to a dermatologist rather than treating as fungus.
  • Green nail syndrome — a distinctly green or blue-green nail, from a bacterium rather than a fungus. It needs different treatment.
  • Lichen planus of the nail — thinning, ridging and sometimes scarring that can destroy the nail permanently. It moves faster than fungus and needs prompt treatment.
  • Onycholysis — the nail simply lifting from the bed after water exposure, chemicals, or aggressive manicures. The space underneath looks white or grey and can then be colonised by fungus, which confuses things further.
  • Yellow nail syndrome — all nails thickened, yellow and slow-growing at once, sometimes with chest or lymphatic problems.
  • Age-related nail change — nails thicken, ridge and yellow with age with no infection at all. Very common, and often the whole answer.
FAQ+
How long does it take for a nail to look normal?Twelve to eighteen months for a big toenail, about six months for a fingernail. That is how long the nail takes to grow out, and it is true even when the fungus was killed in the first few weeks.
Do over-the-counter nail treatments work?Rarely, and only for a small patch on the tip of one nail. Nothing sold over the counter reliably penetrates a thick or fully involved nail. If more than the tip is affected, they are close to a waste of money.
Does Vicks VapoRub work?There is one small study showing some improvement, and it is cheap and harmless, so people do try it. Be clear-eyed about it: the evidence is one small trial with no comparison group, and cure rates are nowhere near those of a prescription. It is a reasonable thing to try on a mild nail you were not going to treat anyway.
Is terbinafine safe?For most healthy people, yes. Serious liver injury is rare. Liver blood tests are checked before and sometimes during treatment. The more common issues are stomach upset and a change in taste or smell, which is usually temporary but occasionally lasts.
Does laser treatment cure it?No. Laser devices are cleared to produce a temporary increase in clear nail, which is a deliberately modest claim. Some people see improvement, cure rates are well below tablets, it usually costs several hundred to a few thousand dollars, and it is rarely covered by insurance.
Do I have to treat it?No. A painless, mildly discoloured nail is a cosmetic issue, and choosing to leave it is reasonable. The situations where treatment matters medically are diabetes, poor circulation, a weakened immune system, or a nail that hurts.
Why is only one nail affected?Because the fungus got in through a specific gap or injury in that nail. It usually spreads to others over years if nothing is done.
Can I wear nail polish?During topical treatment, no — it blocks the medication. During oral treatment it does not interfere, though it hides your only way of judging progress, which is the new growth at the base.
Did I get it at the nail salon?Possibly, if instruments were not sterilised. More often it came from your own athlete's foot. Either way, take your own tools or use a salon that autoclaves theirs.
Will it come back?In roughly one in five people, usually because the athlete's foot on the skin was not treated or the shoes were never dealt with. Antifungal powder in shoes and treating the skin cuts that down a lot.
My nail has a dark brown line in it. Is that fungus?Usually not. Fungus is yellow, white or crumbly. A brown or black band running the length of the nail is pigment, which is often completely harmless — especially on brown and Black skin, and especially if several nails have it. A single new band that is widening or irregular is worth showing to a dermatologist rather than treating.
Can I just have the nail removed?Removing the nail does not kill the fungus in the nail bed, so the new nail usually grows back infected unless antifungal treatment is used as well. It is used mainly when a nail is painful, not as a cure.