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Onychomycosis (Fungal Nail Infection)

Written by Ada’s Medical Knowledge Team

Updated on

What is onychomycosis (fungal nail infection)?

Onychomycosis (also known as tinea unguium) is a fungal nail infection which can affect the toenails and/or fingernails and which occurs in about 10 percent of adults in the United States. Onychomycosis more commonly affects toenails rather than fingernails.

There are several different types of fungal nail infection, depending on the kind of fungus causing the infection. Onychomycosis or infected nails are most often caused by a type of parasitic fungi called dermatophyte fungi.

Most types of onychomycosis have the same signs of infection: the infected nail usually becomes thick and discoloured. This process generally starts at the tip of the nail and progresses downwards towards the root. 1

As the infection progresses, the affected nail can become itchy and/or slightly painful. Infected nails may become crumbly, and it is not uncommon for part or all of the infected nail to break off. Treatment usually involves keeping the nail clean and taking a course of topical antifungal (antimycotic) medication.

Symptoms of fungal nail infection

The first signs of a fungal nail infection are usually perceptible changes to the appearance of the infected nail(s). It is uncommon for an infected nail to cause severe pain or permanent disfigurement, but this does occur in some cases. If left untreated, fungal nail infections can cause difficulties with walking, exercising or manual tasks such as typing. The main symptoms of onychomycosis include the nail becoming:

  • Brittle
  • Broken
  • Discolored
  • Thickened
  • Flaky
  • Lifted away from the nail bed
  • Mildly painful
  • Separated from the nail bed.

These symptoms could also indicate that an individual is suffering from nail psoriasis, a chronic autoimmune skin disease which can affect the skin under the nail. Nail psoriasis is more common in the fingernails than the toenails and can co-occur with fungal infections of the nail.

If you think you may be experiencing the first signs of nail psoriasis or a fungal nail infection, get a free symptom assessment by downloading the Ada app.

Good to know: In people with diabetes, fungal toenail infections can increase the likelihood of developing ulceration and other complications, so medical attention should always be sought if a fungal nail infection is suspected. 2

Types of onychomycosis

Onychomycosis or tinea unguium is usually caused by a buildup of dermatophyte fungi. These are parasitic fungi infecting the skin and nails, which need to reside in human or animal bodies in order to survive. Fungal infections of the nail are caused when dermatophytes burrow under the nails to breed.

Specific types of dermatophytes which commonly cause fungal nail infections include the trichophyton rubrum, the most common type of fungus to infect the nails, and trichophyton interdigitale fungi. Other fungi which can cause fungal nail infections include yeasts, such as the candida albicans and molds, such as scopulariopsis brevicaulis.

What is proximal subungual onychomycosis?

Proximal subungual onychomycosis is the rarest form of fungal nail infection.

Infection usually involves the trichophyton rubrum fungus. Unlike in other kinds of fungal nail infection, infection occurs, initially, at the proximal nail fold (the base of the nail), spreading up the newly developed nail plate.

The proximal subungual form of fungal nail infection usually occurs in people whose immune system is compromised. Proximal subungual onychomycosis is a clinical marker for human immunodeficiency virus (HIV). 3


Wearing tight-fitting socks and shoes, which cause repetitive trauma to the toenails, is a primary cause of fungal nail infections. Onychomycosis is therefore common in people who play a lot of sport, as well as the elderly and anyone with a compromised immune system.

Moist, damp environments serve as breeding grounds for dermatophytes. Healthy people typically catch nail infections from visiting places such as:

  • Communal showers
  • Nail salons and/or foot spas with poorly-cleaned instruments
  • Public swimming pools, jacuzzis and saunas.

How is fungal nail infections diagnosed?

If somebody is suffering from a suspected fungal nail infection, it is advisable to visit the doctor so that they can advise on a treatment plan for the infected nail(s). Fungal nail infections are diagnosed based on the visible symptoms.

Samples of nail clippings are usually sent away for a histopathology examination, the analysis of diseased tissue, in order to identify the presence of dermatophytes and decide on appropriate medication. There is a 30 percent possibility of false negatives when testing for dermatophyte cultures, so it is possible that the test may need to be repeated. 4


Fungal nail infections do not go away on their own, so a course of treatment is always required. This usually involves a combined approach of keeping the affected nails clean to reduce irritation and inflammation, at the same time as following a course of antifungal medication. Onychomycosis is highly infectious, so it is important to begin treatment as soon as possible to minimise the risk of passing the infection to others.

Prevention and management

There are various precautions that one can take in order to reduce the risk of spreading fungal nail infections to others and to increase the chances of a quick recovery. To look after one’s nails and prevent the spread of infection, it is recommended that one:

  • Change one’s socks and shoes regularly
  • Dries one’s hands and feet as soon as possible after exposure to water
  • Files one’s nails to keep the edges smooth
  • Moisturise one’s hands, nails and cuticles daily and after contact with liquids
  • Select shoes and socks made of natural materials, such as cotton
  • Treat skin infections like athlete’s foot promptly to avoid the infection reaching the nails
  • Trim one’s nails regularly
  • Use separate scissors or clippers to tend to infected nails
  • Wear clean, comfortable shoes
  • Wear gloves for housework and other manual tasks


In addition to keeping the site of the infection clean, someone affected by a fungal nail infection may be prescribed topical antimycotics, i.e.antifungal products to apply to the affected area. Topical medications are currently the first-line treatment for fungal nail infections. 4

Topical medications used to treat fungal nail infections

These include:

  • Amorolfine nail lacquer
  • Tioconazole nail solution
  • Ciclopirox

Always use topical antifungal products according to a doctor’s advice and/or follow the guidelines on the packet.

In some cases, all or part of the infected nail may be removed, in order to give the topical medications the best chance to work. This treatment is usually recommended for severe or persistent nail infections. It can be carried out during a regular appointment at the doctor’s office. If the nail is removed surgically, a local anaesthetic will be applied to the affected area before the infected part of the nail is removed. 5

An advantage of surgical removal is that it can be carried out in one appointment, and the course of topical antimycotic medication can then be started. Alternatively, a dressing containing urea can be applied to the affected nail. This must be kept dry for 10 days, during which time the urea will soften the nail, so that it can be removed painlessly by the doctor during a follow-up appointment.

After the nail is removed, topical medications can then be applied. The infection is considered to have cleared up when the new, healthy nail starts to show visible regrowth in the nail bed.

Onychomycosis FAQs

Q: Are there oral medications for fungal nail infections?
A: Oral medications will only be prescribed to treat onychomycosis in cases where topical treatments and self-care alone have been prescribed and have not proven effective in curing the infection. 6 Oral medications for fungal nail infections can cause side effects, which include itching, headaches, diarrhea and a decreased sense of taste. 7

The most common oral antimycotics for onychomycosis are itraconazole and terbinafine, which work by gradually killing the fungi that caused the infection. The doctor will assess a person’s medical history before prescribing these medications, as they may not be suitable for everyone. People who have had liver problems should avoid terbinafine. Itraconazole has been linked to compromised heart function and may react with other medications, including pimozide, quinidine, dofetilide and levacetylmethadol (levomethadyl).

Q: Is it always possible to cure onychomycosis?
A: Onychomycosis can take a long time to treat, and some fungal nail infections can be resistant to antifungal medications. Treating a fungal nail infection can depend on identifying the appropriate medication that is effective against a particular subtype of infection.

Q: Can nail polish cause onychomycosis?
A: Nail polish is a sealant, so it can cause a buildup of moisture behind the nail, potentially creating an environment in which dermatophytes and other microorganisms can thrive. Avoiding nail polish is recommended while undergoing treatment for onychomycosis, as it could reduce the effectiveness of the antifungal medication. Furthermore, the applicator brush could be a vehicle for spreading infectious microorganisms.

Q: What are the main methods for removing a fungal nail?
A: Fungal nails can be removed surgically, using a tool to loosen the skin around the nail and remove the nail after a local anaesthetic is applied to the affected area to prevent pain. If the whole nail is removed, this is called avulsion. If part of the nail is removed, this is called debridement.

Alternatively, the nail can be removed chemically (non-surgically) by placing a dressing containing urea on the nail. This must be kept dry for 10 days after which the nail is softened to the point where it can be removed painlessly by the doctor.

Good to know: It is also possible to treat a fungal nail infection by removing the infected nail using a laser. However, laser treatment for onychomycosis is not usually considered, other than in cases where antifungal medication has been ineffective.

Q: Are fungal nail infections contagious?
A: Fungal nail infections can be passed from one infected nail to another due to direct or indirect contact. For example, toes which are next to one another on the foot may rub together, causing the fungi to spread to skin and infect other nearby nails. A person may also spread their fungal nail infection from one infected nail to other nails by touching it with their hands before touching other areas of the feet or hands and/or through the use of implements which touch multiple fingers or toes, such as nail files or nail polish brushes. People risk catching tinea unguium from one another when they share implements such as these, use public foot-baths or foot-spas, or share shoes or socks.

Q: What are the best home remedies to treat a fungal nail infection?
A: No home remedies for fungal nail infections are currently approved by the Food and Drug Administration (FDA). However, many people report success in reducing the severity of their fungal infection, or curing it altogether by using herbal remedies with antifungal properties, including:

Applying products containing tea tree oil to the affected nail plate(s) and surrounding skinTaking herbal supplements and vitamins, as vitamin deficiencies, in particular being deficient in the B vitamin biotin, can lead to fungal nail infections. If you think you may be affected by a vitamin deficiency, assess your symptoms for free by downloading the Ada app Topical creams and rubs containing ingredients such as menthol, eucalyptus oil, camphor and thymol have been found to treat or cure onychomycosis, in particular, ointments which are traditionally used for decongestion. 8 However, their use in the treatment of fungal nail infections is a recent trend and is not universally medically accepted or FDA-approved. 9

Q: What is the difference between onychomycosis and onycholysis?
A: Although onychomycosis and onycholysis sound similar and are both conditions that affect the nails, these two terms have slightly different meanings:

The definition of onycholysis is the separation of the nail from the skin, which can happen due to a variety of causes, including a single injury or a repetitive trauma, allergic reactions to chemicals such as household cleaning products or nail polish, or as a result of having a fungal nail infection. 10The definition of onychomycosis is a fungal nail infection. This may or may not eventually result in onycholysis if the infected nail becomes sufficiently damaged that it crumbles and breaks away from the skin.

Q: Do fungal nail infections cause pus?
A: The appearance of pus near the nails is more commonly associated with bacterial infections rather than fungal ones. Pus around the nails may indicate that a person is affected by a condition called paronychia, an infection of the skin beside the nail, most often developing in the nail fold. A bacterium called Staphylococcus aureus is a common cause.