Fungal nail infection

Fungal nail infections are usually caused by skin fungi. These infections frequently affect the big toes. As a result, the toenails become discolored or brittle. Fungal nail infections often develop in conjunction with athlete’s foot.

At a glance

  • Fungal nail infections are common. It is estimated that they affect between 3% and 12% of the population.
  • The infection is usually caused by skin fungi.
  • Many people with fungal nail infections also have athlete’s foot.
  • Measures that prevent fungal nail infections from developing include keeping the feet dry, avoiding tight shoes, and wearing flip-flops at the swimming pool and when using communal shower facilities.

Note: The information in this article cannot and should not replace a medical consultation and must not be used for self-diagnosis or treatment.

Fungal nail infection: a woman sits on the floor and looks at her toes.

What is a fungal nail infection?

Fungal nail infections are often caused by an infection with skin fungi: the fungal spores usually become established in a toenail or, less frequently, a fingernail. Over time, the affected nails become cracked and brittle. They also become discolored, appearing yellowish to brownish.

How are fungal nail infections diagnosed?

Discolored nails that appear whitish-yellowish to brownish in color are indicative of a fungal nail infection. Often, the nails thicken and become cracked, brittle and deformed. Over time, the affected part of the nail becomes detached from the nail bed. The nails can also hurt.

Symptoms of a fungal nail infection include, for example, spots on the big toenail or white superficial fungal nail infection on several toenails.

Fungal nail infections very commonly affect the nails on the big toes, and specifically the tops and sides of these nails. Less often, the site of infection is the nail root. This is more likely to occur in people with a significantly compromised immune system, as is possible with diabetes, for example.

What causes fungal nail infections?

Fungal nail infections are usually caused by skin fungi. However, they can also be due to a mold fungus or yeast fungus. A yeast fungus is more likely to affect the fingernails. Fungal nail infections frequently occur in conjunction with athlete's foot. It is thought that fungal nail infections often occur as a result of athlete’s foot. 

What are the risk factors for fungal nail infection?

It is not yet clear what exactly increases the risk of a fungal nail infection. However, the following factors are generally thought to play a part:

  • existing athlete’s foot
  • frequent visits to swimming pools or saunas 
  • nail injuries
  • tight footwear
  • some skin conditions, such as psoriasis
  • circulatory disorders in the legs, e.g., caused by diabetes or peripheral artery disease (PAD) 
  • a weakened immune system – either due to illness or as a result of taking certain medications (known as immunosuppressives) that suppress the functions of the immune system
  • the transmission of a fungal nail infection within the family

Fungal nail infections on the hands primarily affect people who frequently get their hands wet (e.g., cleaning personnel). 

How common are fungal nail infections?

Approximately 3 to 12% of the population have a fungal nail infection. Older people are affected more often than younger people.

Approximately 3 to 12% of the population have a fungal nail infection.

What is the outlook for a fungal nail infection?

For people who are otherwise healthy, a fungal nail infection is harmless but rarely goes away of its own accord. Without treatment, it may either remain confined to or spread beyond the area of nail where it originated. However, it is not known how often this occurs.

If the individual has diabetes or a weakened immune system, a fungal nail infection may lead to a bacterial infection of the surrounding skin areas. It may also cause problems when walking if the nail becomes thickened and painful.

What can be done to prevent a fungal nail infection?

It is thought that fungal nail infections are often caused by athlete’s foot. This means that measures to prevent athlete’s foot can also help to prevent a fungal nail infection. Fungus tends to thrive in damp environments, and so it is particularly important to keep the feet dry.

Fungal nail infections can be prevented by drying the feet thoroughly, wearing breathable shoes, washing at a minimum temperature of 60°, wearing flip-flops at the swimming pool.

Ways to do this include:

  • carefully drying the feet after showering, bathing, or swimming – ideally using both a towel and a hair dryer
  • wearing shoes that aren’t too tight and allow the feet to breathe
  • removing footwear as often as possible
  • wearing flip-flops in communal shower areas, swimming pools, and saunas
  • avoiding sharing of shoes and towels with others
  • washing socks, bed linen, and towels at 60 degrees or higher

In addition to damp feet, nail injuries can also make fungal nail infections more likely to develop. If the feet are exposed to strain for longer periods, for example, during a long hike or jog, it is particularly important to wear shoes that fit well and are not too tight, as well as special sports socks or hiking socks to prevent excessive pressure on the feet.

How is a fungal nail infection diagnosed?

It is not always easy to detect a fungal nail infection at first glance as it may have a very similar appearance to psoriasis of the nails, for example. If a fungal nail infection is suspected, doctors will scrape off a sample of the affected nail and have it examined under the microscope in a lab.

A special dye is used to color the tissue sample for this purpose. However, to determine the precise type of fungus that is causing the infection, a fungal culture needs to be grown in a lab. This process takes about 3 weeks. Less commonly, additional laboratory testing is undertaken, for example to examine the nail tissue in more detail.

How is a fungal nail infection treated?

Fungal nail infections are persistent, especially when they affect the toenails as these grow much more slowly than fingernails.

As a result, treatment requires patience. In some cases, it may take several months for a visible improvement to occur. However, patience and continuous treatment usually pay off, and a healthy nail will begin to grow, while the infected portion of nail will simply grow out. Targeted treatment can also prevent thickening of the nail and a spread of the infection.

A special, clear nail polish can be used to externally treat the fungal nail infection. This can be obtained over the counter (i.e. without a prescription) from pharmacies and usually contains the active ingredient amorolfine or ciclopirox. These inhibit growth of the fungus or kill it completely. It is important for this topical treatment to be applied regularly and consistently.

Besides nail polishes, special kits are available for treating fungal nail infections. These contain a urea-based cream, which is used first to soften the infected area, and a spatula, which is used to scrape it away. The skin underneath the nail then needs to be treated for several weeks with a cream containing the active ingredient bifonazole.

These topical treatments with nail polishes and ointments are only effective to a certain extent. Tablets may also need to be taken in order to clear up a fungal nail infection completely. This medication, which is available on prescription, usually contains itraconazole or terbinafine. The treatment prescribed depends, for example, on which fungus is causing the infection.

Important: With fungal toenail infections, medication usually has to be taken for more than 12 weeks, whereas a treatment period of 6 weeks may be sufficient for fungal infections of the fingernails. It is also important to be aware that these tablets may have side effects, such as gastrointestinal upset.

Household remedies, such as applying tea tree oil or vinegar, are sometimes also recommended as treatments for fungal nail infections. However, the effectiveness of these and other remedies against fungal nail infections has not yet been proven in well-conducted studies.

More detailed information on how fungal nail infections can be treated can be found at

In cooperation with the Institute for Quality and Efficiency in Health Care (Institut für Qualität und Wirtschaftlichkeit im Gesundheitswesen) (IQWiG).

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