Infectious Diseases A to Z – Onychomycosis (tinea unguium)

With this new column, Elite Healthcare will compile an index of various infectious diseases, with occasional highlights of emerging conditions.

Onychomycosis (tinea unguium)

General definition and information:

Better known as a fungal infection of the nail(s), onychomycosis is a common ailment that can cause fingernails and, more prominently, toenails to become discolored, thick, and more likely to crack and break. Sometimes linked to patients who also have a fungal skin infection on the foot, especially between the toes (aka “athlete’s foot”), onychomycosis is one of several fungal diseases identified cy the Centers for Disease Control and Prevention CDC).1 Also more common among those who’ve suffered a nail injury, have had nail surgery, have been diagnosed with diabetes, or have a weakened immune system and/or blood circulation problem, the condition is marked by discolored (yellow, brown, or white) nails, thickened nails, and nails that are fragile or cracked. Diagnosed on assessment or by clipping the nail clipping to have a laboratory culture performed, the condition is not expected to be painful unless severe, which is likewise uncommon. However, severity can be a concern specifically for the diabetic patient population, if the infection spreads to the skin, causes the skin to crack, and leads to the development of cellulitis.

Causes & Modes of Transmission:

Caused by many different types of fungi (yeasts or molds) that live in the environment, onychomycosis settles in when small cracks in the nail or the surrounding skin allow germs to enter the nail and cause an infection. The CDC defines onychomycosis based on the following origins of infection.1

  • Distal or lateral subungual onychomycosis: Most common form; highlighted by yellowish, brownish, or whitish discoloration that begins under the distal edge or sides of the nail and spreads over the entire nail plate. The big toenail is most often affected, but all nails are susceptible.
  • Proximal subungual onychomycosis: Infection originates from the proximal nail fold and spreads distally. Trichophyton rubrum, a dermatophytic fungus, is the primary causative agent in the United States.
  • Superficial onychomycosis: When fungi invade the superficial layers of the nail plate and spread deeper into the nail plate as the infection progresses. Lesions are often white and are most often caused by Trichophyton mentagrophytes (athlete’s foot).
  • Endonyx onychomycosis: The nail bed is not involved in this infection; only the interior of the nail plate is infected.
  • Totally dystrophic onychomycosis: Often a sign of end-stage distal or proximal subungual onychomycosis. The nail bed is thickened and raised with copious keratotic debris.
  • Yeast onychomycosis: Affects fingernails more commonly than toenails and is often caused by Candida. May be a sign of underlying immunodeficiency.
  • Fungal melanonychia:2 An uncommon nail infection caused by melanin-producing molds such as Scytalidium, Alternaria, and Exophiala, causing brownish or blackish discolorations of the nail plate. May present similar to subungual melanoma.

Treatment Strategies:

Fungal nail infections can be difficult to cure and typically do not resolve without antifungal treatment, according to the CDC, which suggests prescription antifungal pills as the best line of treatment. Severe cases may lead to the removal of the nail, which can still result in several months being needed for the infection to be cured. Self-care strategies and over-the-counter products can also be considered, and repeat infections are common, according to the Mayo Clinic. According to the CDC, topical antifungal agents can be used but are often ineffective. Oral terbinafine is considered to be the first-line treatment, with a treatment course of generally six weeks for fingernails and 12 weeks for toenails.3 Azoles can also be used, and surgical debridement or removal of the affected nail is a consideration for cases that are resistant to antifungals, according to the CDC, which also reports that laser treatments appear to be a promising area for future study.4

Prevention Parameters:

The CDC suggests that healthcare providers encourage patients to take the following prevention practices:

  • Keep hands and feet clean and dry.
  • Clip fingernails and toenails short, and keep them clean.
  • Don’t walk barefoot in areas like locker rooms or public showers.
  • Don’t share nail clippers with other people.
  • When visiting a nail salon, choose one that is clean and licensed by a state cosmetology board. Ensure the salon sterilizes its instruments after each use or carry in personal instruments from home. Please click here for more information about nail hygiene.
  • Scrub the underside of nails with soap and water (or a nail brush) when handwashing.
  • Clean any nail grooming tools before use.
  • Avoid biting or chewing nails.
  • Avoid cutting cuticles, which act as barriers to prevent infection.
  • Never rip or bite hangnails. Clip them with a clean, sanitized nail trimmer.


  1. Fungal nail infections. CDC. 2017. Accessed online:
  2. Finch J, Arenas R, Baran R. Fungal melanonychia. J Am Acad Dermatol. 2012;66(5):830-41.
  3. Lipner S, Scher RK. Onychomycosis: current and future therapies. Cutis. 2014;93(2):60-3.
  4. Gupta AK, Paquet M, Simpson FC. Therapies for the treatment of onychomycosis. Clin Dermatol. 2013;31(5):544-54.

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