Fungal Nail Infections
Fungal nail infections, also known as “onychomycosis,” are very common. They may affect up to 14% of the general population. Fungal toenail infections are more common than fungal fingernail infections.1
Most fungal nail infections are not serious. However, some people may experience pain or be bothered by the appearance of their nails.
Fungal nail infections may cause nails to become discolored, thick, fragile, or cracked. The nail may also become separated from the nail bed.
People who have fungal toenail infections often have a fungal skin infection on the foot, especially between the toes (commonly called athlete’s foot, ringworm on the foot, or tinea pedis).
How does someone get a fungal nail infection?
Fungal nail infections are caused by many different types of fungi that live in the environment. Small cracks in your nail or the surrounding skin can allow these germs to enter your nail and cause an infection.
Who gets fungal nail infections?
- A nail injury or foot deformity
- Weakened immune system (for example, because of cancer)
- Venous insufficiency (poor circulation in the legs) or peripheral arterial disease (narrowed arteries reduce blood flow to the arms or legs)
- Fungal skin infections on other parts of the body
Occasionally, a bacterial infection can occur on top of a fungal nail infection and cause serious illness. This is more common in people with diabetes or other conditions that weaken the body’s defenses against infection.
- Keep your hands and feet clean and dry.
- Keep fingernails and toenails short and 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 a salon that is clean and licensed by your state’s cosmetology board. Make sure the salon sterilizes its instruments (nail clippers, scissors, etc.) after each use, or bring your own.
Fungal infections are not the only possible cause of nail problems. Other conditions can look similar to fungal nail infections.
Your healthcare provider should generally confirm your diagnosis using laboratory testing before prescribing antifungal treatment. To confirm the diagnosis, the healthcare provider might collect a nail clipping to look at under a microscope or to send to a laboratory for testing.
Fungal nail infections can be difficult to cure, and treatment is most successful when started early. Fungal nail infections typically don’t go away on their own, and the best treatment is usually prescription antifungal pills taken by mouth. In severe cases, a healthcare professional might remove the nail completely. It can take several months to a year for the infection to go away.
Fungal nail infections can be closely associated with fungal skin infections. If a fungal infection is not treated, it can spread from one place to the other. Patients should discuss all skin concerns with their healthcare provider to ensure that all fungal infections are properly treated.
Even after treatment, fungal nail infections can come back. This is more common in people who have conditions like diabetes that make them more likely to get a fungal nail infection. If you suspect an infection has returned, contact your healthcare provider.
Information for healthcare professionals
Onychomycosis can be difficult to diagnose based on physical appearance and clinical history alone. Clinicians should confirm a diagnosis of onychomycosis by laboratory testing before prescribing antifungal medications. The following types of laboratory tests can confirm the diagnosis of onychomycosis:
- Microscopy: Potassium hydroxide (KOH) stain can be performed in the office setting, but the accuracy of the test depends on clinician experience and technique. Nail clippings or scrapings are placed in a drop of KOH and examined under a microscope for the presence of fungal elements.3
- Histopathologic examination with a periodic acid-Schiff (PAS) stain: Examination of nail clippings with a PAS stain can confirm the diagnosis of a fungal nail infection.
- Culture:Fungal culture can be used to identify the infecting organism, but the fungi may take several weeks to grow. 4,8
- Molecular: Molecular testing, including polymerase chain reaction (PCR) testing, may be used to diagnose fungal nail infections.
Antimicrobial-resistant onychomycosis is a growing problem.13-15 Therefore, antifungal susceptibility testing may be considered based on the fungus or fungi identified and the patient’s clinical course.12,16,17
Oral antifungal therapy should be prescribed only after confirmation of fungal infection. Oral terbinafine is typically the first-line treatment for confirmed onychomycosis. The treatment course is generally 6 weeks for fingernails and 12 weeks for toenails.9 Given increasing reports of terbinafine resistance in onychomycosis, the possibility of resistance should be considered if patients do not improve with therapy. Identification and susceptibility testing of the causative fungus or fungi may help guide therapy. Note, however, that antimicrobial resistance is not the only possible reason for treatment failure.17 Clinicians should also consider the possibility of incorrect diagnosis or inadequate patient adherence to therapy.
Topical antifungal agents can be used but are often ineffective. Systemic azoles can also be used. Surgical debridement or removal of the affected nail is also a consideration for cases that are resistant to antifungals, and laser treatments for onychomycosis appear to be a promising area for future study.10
Recurrence is common among patients with onychomycosis.18 To minimize recurrence, clinicians should educate patients about prevention methods (e.g., keeping hands and feet clean and dry) and early signs of disease. Patients should also be aware of the association between onychomycosis and tinea pedis and promptly seek treatment for other tinea lesions.
- Gupta AK, Jain HC, Lynde CW, Macdonald P, Cooper EA, Summerbell RC. Prevalence and epidemiology of onychomycosis in patients visiting physicians’ offices: a multicenter Canadian survey of 15,000 patients. J Am Acad Dermatol. 2000 Aug;43(2 Pt 1):244-8.
- Scher RK, Rich P, Pariser D, Elewski B. The epidemiology, etiology, and pathophysiology of onychomycosis. Semin Cutan Med Surg. 2013 Jun;32(2 Suppl 1):S2-4.
- Gupta AK, Konnikov N, MacDonald P, Rich P, Rodger NW, Edmonds MW, et al. Prevalence and epidemiology of toenail onychomycosis in diabetic subjects: a multicentre survey. Br J Dermatol. 1998 Oct;139(4):665-71.
- Elewski BE. Onychomycosis: pathogenesis, diagnosis, and management. Clin Microbiol Rev. 1998 Jul;11(3):415-29.
- Hay RJ, Baran R. Onychomycosis: a proposed revision of the clinical classification. J Am Acad Dermatol. 2011 Dec;65(6):1219-27.
- Finch J, Arenas R, Baran R. Fungal melanonychia. J Am Acad Dermatol. 2012 May;66(5):830-41.
- Wilsmann-Theis D, Sareika F, Bieber T, Schmid-Wendtner MH, Wenzel J. New reasons for histopathological nail-clipping examination in the diagnosis of onychomycosis. J Eur Acad Dermatol Venereol. 2011 Feb;25(2):235-7.
- Elewski BE, Leyden J, Rinaldi MG, Atillasoy E. Office practice-based confirmation of onychomycosis: a US nationwide prospective survey. Arch Intern Med. 2002 Oct 14;162(18):2133-8.
- Onychomycosis: current and future therapies. Cutis. 2014 Feb;93(2):60-3.
- Gupta AK, Paquet M, Simpson FC. Therapies for the treatment of onychomycosis. Clin Dermatol. 2013 Sep-Oct;31(5):544-54.
- Ghannoum MA, Hajjeh RA, Scher R, Konnikov N, Gupta AK, Summerbell Ret, al. A large-scale North American study of fungal isolates from nails: the frequency of onychomycosis, fungal distribution, and antifungal susceptibility patterns. J Am Acad Dermatol. 2000 Oct;43(4):641-8
- Gu D, Hatch M, Ghannoum M, Elewski BE. Treatment-resistant dermatophytosis: A representative case highlighting an emerging public health threat. JAAD. 2020 November; 6(11):1153-1155.
- Saunte DML, Hare RK, Jorgensen KM, Jorgensen R, Deleuran M, Zachariae CO, et al. Emerging Terbinafine Resistance in Trichophyton: Clinical Characteristics, Squalene Epoxidase Gene Mutations, and a Reliable EUCAST Method for Detection. Antimic Agent and Chemo. 2019 Sept; 63(10).
- Gupta AK, Renaud HJ, Quinlan EM, Shear NH, Piguet V. The Growing Problem of Antifungal Resistance in Onychomycosis and Other Superficial Mycoses. Am J Clin Dermatol. 2021 Mar;22(2):149-157.
- Astvad KMT, Hare RK, Jørgensen KM, Saunte DML, Thomsen PK, Arendrup MC. Increasing Terbinafine Resistance in Danish Trichophyton Isolates 2019–2020. Journal of Fungi. 2022; 8(2):150.
- Ebert A, Monod M, Salamin K, Burmester A, Uhral ß S, Wiegand C, et al. Alarming India-wide phenomenon of antifungal resistance in dermatophytes: A multicentre study. 2020 Jul; 63(7):717-728.
- Gupta AK, Venkataraman M, Renaud HJ, Summerbell R, Shear NH, Piguet V. A Paradigm Shift in the Treatment and Management of Onychomycosis. Skin Append Disord. 2021;7(5).
- Tosti A, Elewski BE. Onychomycosis: Practical Approaches to Minimize Relapse and Recurrence. Skin Appendage Disord. 2016 Sep;2(1-2):83-87.