Fungal Nail Infection
Reviewed by Andrew Schox, BSc(Hons) PGradDipPod MPod, October 2026
Fungal nail infection (onychomycosis) is the most common nail problem, making up about half of all nail disease. Estimates of how many people have it range from under 1 per cent to 28 per cent. The nail may turn white, yellow or brown, thicken, crumble or lift. It can be treated, but it takes months, it doesn't always work, and the nail may never look completely normal again. A nail test is needed first, because other conditions can look the same.
What is it?
Fungal nail infection is an infection of the nail caused by a fungus. The fungi involved are dermatophytes (a group of fungi that often infect skin, hair and nails), yeasts and moulds. It is the most common nail problem, making up about 50 per cent of all nail disease.
The infection can make the nail change colour, thicken and come away from the nail bed (the skin under the nail). The skin around the nail is often affected too.
Who does it affect?
How common it is depends on the country, the person's age and the fungus involved. Estimates range from under 1 per cent to 28 per cent. In Europe and North America the average is about 4.3 per cent. It may be less common than some figures suggest, because figures from hospital clinics can overstate it.
You are more likely to get it if you are older, have diabetes or have a weakened immune system (your body's defence against infection). Problems from the infection are also more common in people with poor blood flow to the legs and feet, and in people with a weakened immune system. In people with diabetes they can be serious.
Signs and symptoms
Early on, you may notice nothing at all. As the infection grows, the nail can turn white, yellow, orange, brown or black. It may thicken, become misshapen, brittle or crumbly, and be hard to cut. Some people see streaks of colour, flaking or pitting on the nail surface, or a smelly white, yellow or green discharge. The nail may lift off the nail bed and may be sore under pressure from shoes.
A yellow, thick, crumbly nail is often fungal, but not always. Nail psoriasis (a skin condition that also affects nails) is another common cause of a yellow nail.
What causes it?
Most cases are caused by dermatophytes, which cause about 65 per cent of infections. The most common single fungus is Trichophyton rubrum. Yeasts and moulds cause the rest, and they play a bigger part in fingernail infections.
These are largely the same fungi that cause athlete's foot (a fungal skin infection of the feet, also called tinea pedis). They live on the skin and multiply in warm, moist, dark places, such as inside shoes. Infection gets in through the skin, usually starting at the tip of the nail. Athlete's foot that isn't treated early can spread to the toenails. The infection can also pass from person to person.
How is it diagnosed?
Your podiatrist will look at your nails and the skin of your feet. Because other conditions can look the same, including psoriasis, lichen planus (an itchy skin and nail condition) and nail injury, looking is not enough.
The diagnosis should be confirmed by sending a nail sample to a laboratory. The usual tests are microscopy (looking at the sample under a microscope) and culture (growing the fungus in the lab). Culture is slow, because the fungus grows slowly. When both tests are done, at least one is positive in about 80 per cent of people who have the infection. A negative result doesn't always rule out infection, so you may need a second sample if your podiatrist still suspects a fungus.
Treatment
Not everyone needs treatment, and it won't always work. Your podiatrist or GP can talk through your options with you.
Looking after it at home
Treat athlete's foot early, so it doesn't spread to your nails. The infection gets in through the skin, so caring for the skin of your feet matters as much as caring for the nail. Clean or replace shoes, socks and other textiles that may carry the fungus.
Treatment from your podiatrist
Your podiatrist can check your nails and feet, take a nail sample for testing, and treat any athlete's foot. They can also help you decide when to see your GP or a specialist.
Tablets for fungal nails (terbinafine or itraconazole) need a prescription, so a GP or another prescriber will decide if they suit you. You should have a laboratory-confirmed diagnosis first, because different fungi respond differently to antifungal medicines. Tablets are taken for at least three months, and sometimes for 9 to 12 months. Both medicines can affect the liver, so you will have blood tests before you start and again about one month in. Treatment is stopped if the results are abnormal.
Both medicines can interact with other medicines. Terbinafine shouldn't be taken with some medicines, including phenothiazines and pimozide. Tell your prescriber about any health conditions, allergies, medicines you take, and whether you are pregnant or breastfeeding. Children's doses usually depend on their age, so children need advice from a pharmacist or GP.
Other options
If treatment hasn't worked, your GP or podiatrist should first check that the diagnosis was confirmed by a laboratory test. You may then be referred to a nail or skin specialist. A referral is also suggested if the infection has spread to other nails, the nail is badly affected, or you have another condition such as psoriasis or diabetes. Which treatments work best after first-line care has failed isn't yet clear.
Recovery
Tablets don't always work, and even when they do, the nail may never return fully to normal. Expect a long course, usually at least three months of tablets.
A dark band or streak in a nail is not a sign of slow recovery. It needs to be checked separately (see below). Most dark bands in children's nails turn out to be harmless, but they still need careful checking and follow-up over time.
Preventing it
Treat athlete's foot early. Look over the places your feet spend time, and your shoes and socks. Clean shoes, socks, stockings and other textiles that may carry the fungus. This helps stop the infection coming back and spreading.
If you notice nail changes and you have diabetes, poor circulation or a weakened immune system, have them checked early rather than waiting.
When to see a podiatrist
Book an appointment if
Your nail has become discoloured, thick, crumbly or lifted, or it is uncomfortable in shoes or worrying you. Also book if you have athlete's foot that isn't clearing, if treatment hasn't worked, or if the infection has spread to other nails (ask about a referral to a nail specialist). If you have diabetes, poor circulation or a weakened immune system, book with your podiatrist or GP soon about any nail change, because problems are more likely.
Seek prompt assessment if
See your GP soon, and don't wait to see whether antifungal treatment works, if you have a dark streak or band down a nail (especially one that widens, darkens or spreads to the skin around the nail), or bleeding in the same spot under a nail that keeps happening. Also see your GP soon if your nails change in colour, texture, shape or thickness and you don't know why, or if the skin around a nail becomes painful, infected or has pus (your pharmacist can also advise). See a doctor today if your foot quickly becomes more painful or red, or you feel unwell. If your GP can't see you today, go to an urgent care clinic or an after-hours GP. If you are taking terbinafine and your skin or the whites of your eyes turn yellow, or you have pale stools and dark urine, stop taking it and see a doctor straight away. If you have swelling of the face, neck or tongue, or a severe skin reaction with peeling or blistering while on antifungal medicine, get urgent medical help today. Call your local emergency number if you also have trouble breathing.
Frequently asked questions
Do I have to treat a fungal nail?
Not always. Treatment is usually advised when the nail is uncomfortable (for example, walking hurts), when it distresses you, or when you have diabetes, vascular disease (poor blood flow) or a connective tissue disorder. These put you at higher risk of a bacterial infection or cellulitis (a skin infection) in the foot.
Why do I need a nail test before tablets?
Because psoriasis, lichen planus and injury can look just like a fungus, and tablets won't help those. Different fungi also respond differently to antifungal medicines. Knowing exactly what you have lets your prescriber choose treatment that makes sense, and avoids the risks of tablets when you don't need them.
Can I pass it to other people in my home?
Yes, the infection can spread between people who live together. If someone in your home has a fungal nail or skin infection, keep an eye on your own feet and nails. It isn't clear how much of this is shared surroundings and how much is shared susceptibility.