Fungal nail infection

What is a fungal nail infection?

A fungal nail infection (onychomycosis) is an infection of the nail caused by fungi. It's the most common nail problem, making up about half of all nail disease¹. It typically causes discolouration, thickening and lifting of the nail, and the skin around it can be affected too².

How many people have it depends on the country, age and type of fungus. In studies of the general population in Europe and North America, about 4% of people had it³. Hospital studies give higher figures, but these probably overstate how common it is³.

What causes it, and who gets it?

Most fungal nail infections are caused by dermatophytes (a group of fungi), mainly one called Trichophyton rubrum⁴. These are largely the same fungi that cause athlete's foot. They can live harmlessly on skin, but multiply in warm, moist, dark places such as inside shoes⁵. Athlete's foot can spread to the toenails if it isn't treated early⁶.

The infection can also pass between people who live together: it's been seen in almost half of households with someone affected⁷. If someone at home has a fungal nail or skin infection, keep an eye on your own feet and nails.

People with diabetes or a weakened immune system are at higher risk⁸. Complications are more common with poor circulation (peripheral vascular disease) or a weakened immune system, and in people with diabetes they can threaten the limb⁴.

What does it look like, and how is it diagnosed?

Early on there may be no symptoms. Later the nail can turn white, yellow, orange, brown or black, thicken, crumble or lift, and it may be uncomfortable in shoes⁵.

Skin conditions such as psoriasis and lichen planus, or an injury to the nail, can look just like fungus⁷, so how a nail looks isn't enough to go on. The diagnosis should be confirmed by testing a nail sample in a laboratory⁴. No test is perfect, and a negative result doesn't always rule out infection, so a repeat sample may be needed if the suspicion stays high⁴.

What helps first?

If you have athlete's foot, treating it early is a good first step, because it can spread to the nails⁶. Treatment for the nail itself is usually advised when the nail is uncomfortable, when how it looks upsets you, or when you have diabetes, vascular disease or a connective tissue disorder, because of a higher risk of skin infection (cellulitis)⁶.

A podiatrist or GP can take a nail clipping for testing. Antifungal tablets shouldn't be prescribed until a laboratory test has confirmed the infection⁹. Because tablets can affect the liver, you'll need blood tests before and during treatment⁵. Tell your GP or pharmacist about any health conditions, allergies, other medicines, and pregnancy or breastfeeding, as many antifungals aren't suitable¹⁰. It isn't clear yet which first treatment works best, so talk through the options with your GP.

What if that isn't enough?

If a nail hasn't improved, ask your GP or podiatrist to check that the diagnosis was confirmed by a laboratory test⁹. It isn't clear yet which treatment works best once the first one has failed, so this is a conversation to have with your GP.

Referral to a dermatologist (a skin doctor) is recommended if the infection isn't responding, the diagnosis is uncertain, or a growth under the nail is suspected⁹. It's also recommended if the infection has spread to other nails, is severe, has reached the nail matrix (where the nail grows from), or you have diabetes or psoriasis⁷.

How long does it take, and how can I stop it coming back?

Antifungal tablets are taken for at least three months, sometimes 9–12 months⁵. They don't always work, and the nail may never return fully to normal⁵.

To help stop it coming back, look beyond the nail, because infections enter through the skin¹¹. Treat athlete's foot early⁶. Cleaning shoes, socks, stockings and other textiles is described as an important part of preventing the infection returning and spreading¹¹.