(See also Overview of Nail Disorders Overview of Nail Disorders A variety of disorders can affect nails, including deformities, infections of the nail, paronychia, and ingrown toenails. Nail changes may occur in many systemic conditions and genetic syndromes... read more .)
About 10% (range 2 to 14%) of the population has onychomycosis.
Risk factors for onychomycosis include
Exposure to someone with tinea pedis or onychomycosis (eg, a family member or through public bathing)
Peripheral vascular disease Peripheral Arterial Disease Peripheral arterial disease (PAD) is atherosclerosis of the extremities (virtually always lower) causing ischemia. Mild PAD may be asymptomatic or cause intermittent claudication; severe PAD... read more or diabetes Diabetes Mellitus (DM) Diabetes mellitus is impaired insulin secretion and variable degrees of peripheral insulin resistance leading to hyperglycemia. Early symptoms are related to hyperglycemia and include polydipsia... read more
Toenails are 10 times more commonly infected than fingernails. About 60 to 80% of cases are caused by dermatophytes Overview of Dermatophytoses Dermatophytoses are fungal infections of keratin in the skin and nails (nail infection is called tinea unguium or onychomycosis). Symptoms and signs vary by site of infection. Diagnosis is by... read more (eg, Trichophyton rubrum); dermatophyte infection of the nails is called tinea unguium. Many of the remaining cases are caused by nondermatophyte molds (eg, Aspergillus, Scopulariopsis, Fusarium). Immunocompromised patients and those with chronic mucocutaneous candidiasis Candidiasis (Mucocutaneous) Candidiasis is skin and mucous membrane infection with Candida species, most commonly Candida albicans. Infections can occur anywhere and are most common in skinfolds, digital web spaces, genitals... read more may have candidal onychomycosis (which is more common on the fingers). Subclinical onychomycosis can also occur in patients with recurrent tinea pedis Tinea Pedis (Athlete's Foot) Tinea pedis is a dermatophyte infection of the feet. Diagnosis is by clinical appearance and sometimes by potassium hydroxide wet mount, particularly if the infection manifests as hyperkeratotic... read more . Onychomycosis may predispose patients to lower extremity cellulitis.
Symptoms and Signs of Onychomycosis
Nails have asymptomatic patches of white or yellow discoloration and deformity. There are 3 common characteristic patterns:
Distal subungual: The nails thicken and yellow, keratin and debris accumulate distally and underneath, and the nail separates from the nail bed (onycholysis Onycholysis Deformities are often considered together with dystrophies, but the two are slightly different; deformities are generally considered to be gross changes in nail shape, whereas dystrophies are... read more ).
Proximal subungual: A form that starts proximally and is a marker of immunosuppression.
White superficial: A chalky white scale slowly spreads beneath the nail surface.
Diagnosis of Onychomycosis
Potassium hydroxide wet mount examination
Culture or polymerase chain reaction (PCR)
Histopathologic examination of periodic acid-Schiff (PAS)–stained nail clippings and subungual debris
(See also an update on the current approaches to diagnosis and treatment of onychomycosis.)
Onychomycosis is suspected by appearance in patients who also have tinea pedis Tinea Pedis (Athlete's Foot) Tinea pedis is a dermatophyte infection of the feet. Diagnosis is by clinical appearance and sometimes by potassium hydroxide wet mount, particularly if the infection manifests as hyperkeratotic... read more ; predictive clinical features include involvement of the 3rd or 5th toenail, involvement of the 1st and 5th toenails on the same foot, and unilateral nail deformity. Subclinical onychomycosis should be considered in patients with recurrent tinea pedis.
Differentiation from psoriasis Psoriasis Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including... read more or lichen planus Lichen Planus Lichen planus is a recurrent, pruritic, inflammatory eruption characterized by small, discrete, polygonal, flat-topped, violaceous papules that may coalesce into rough scaly plaques, often accompanied... read more is important because the therapies differ, so diagnosis is typically confirmed by microscopic examination and, unless microscopic findings are conclusive, culture of scrapings or PCR of clippings. Scrapings are taken from the most proximal position that can be accessed on the affected nail and are examined for hyphae on potassium hydroxide wet mount and cultured. Although more expensive, PCR has become a more common technique to confirm the diagnosis of onychomycosis, especially if cultures are negative or a definitive diagnosis is required (1 Diagnosis references Onychomycosis is fungal infection of the nail plate, nail bed, or both. The nails typically are deformed and discolored white or yellow. Diagnosis is by appearance, wet mount, culture, polymerase... read more , 2 Diagnosis references Onychomycosis is fungal infection of the nail plate, nail bed, or both. The nails typically are deformed and discolored white or yellow. Diagnosis is by appearance, wet mount, culture, polymerase... read more , 3 Diagnosis references Onychomycosis is fungal infection of the nail plate, nail bed, or both. The nails typically are deformed and discolored white or yellow. Diagnosis is by appearance, wet mount, culture, polymerase... read more ). Histopathologic examination of PAS–stained nail clippings and subungual debris may also be helpful.
Obtaining an adequate sample of nail for culture can be difficult because the distal subungual debris, which is easy to sample, often does not contain living fungus. Therefore, removing the distal portion of the nail with clippers before sampling or using a small curette to reach more proximally beneath the nail increases the yield.
1. Joyce A, Gupta AK, Koenig L, et al: Fungal Diversity and Onychomycosis: An analysis of 8,816 toenail samples using quantitative PCR and next-generation sequencing. J Am Podiatr Med Assoc 109(1):57–63, 2019. doi: 10.7547/17-070.
2. Haghani I, Shams-Ghahfarokhi M, Dalimi Asl A, et al: Molecular identification and antifungal susceptibility of clinical fungal isolates from onychomycosis (uncommon and emerging species). Mycoses 62(2):128–143, 2019. doi: 10.1111/myc.12854.
3. Gupta AK, Mays RR, Versteeg SG, et al: Update on current approaches to diagnosis and treatment of onychomycosis. Expert Rev Anti Infect Ther 16(12):929–938, 2018. doi: 10.1080/14787210.2018.1544891.
Treatment of Onychomycosis
Selective use of oral terbinafine or itraconazole
Occasional use of topical treatments (eg, efinaconazole, tavaborole, ciclopirox 8%, amorolfine)
Onychomycosis is not always treated because many cases are asymptomatic or mild and unlikely to cause complications, and the oral drugs that are the most effective treatments can potentially cause hepatotoxicity and serious drug interactions. Some proposed indications for treatment include the following:
Presence of bothersome symptoms
Desire for cosmetic improvement (controversial)
Treatment of onychomycosis is typically oral terbinafine or itraconazole. Terbinafine 250 mg once a day for 12 weeks (6 weeks for fingernail) or pulse therapy with 250 mg once a day for 1 week a month until the nail is clear achieves a cure rate of 75 to 80% and itraconazole 200 mg 2 times a day 1 week a month for 3 months achieves a cure rate of 40 to 50%, but the overall recurrence rate is estimated to be as high as 10 to 50%. It is not entirely necessary to treat until all abnormal nail is gone because these drugs remain bound to the nail plate and continue to be effective after oral administration has ceased; however, risk of recurrence may be higher in such cases. The affected nail will not revert to normal, but newly growing nail will appear normal. Fluconazole may also be an option.
The newer topical agents efinaconazole and tavaborole can penetrate the nail plate and are more effective than older topical agents.
Investigative treatments include new delivery systems for terbinafine. Topical antifungal nail lacquer containing efinaconazole 10%, ciclopirox 8%, or amorolfine 5% (not available in the US) is occasionally effective as primary treatment (cure rate of about 30%) and can improve cure rate when used as an adjunct with oral drugs, particularly in resistant infections.
To limit relapse, the patient should trim nails short, dry feet after bathing, wear absorbent socks, and use antifungal foot powder. Old shoes may harbor a high density of spores and, if possible, should not be worn.
Onychomycosis is highly prevalent, particularly among older men and patients with compromised distal circulation, nail dystrophies, and/or tinea pedis.
Suspect the diagnosis based on appearance and the pattern of nail involvement and confirm it by microscopy and culture or PCR.
Treatment is warranted only if onychomycosis causes complications or troublesome symptoms.
If treatment is warranted, consider terbinafine (the most effective treatment) and measures to prevent recurrence (eg, limiting moisture, discarding old shoes, trimming nails short).