onychomycosis

Last edited 07/2021 and last reviewed 11/2022

Onychomycosis is an infection of the nail caused by fungi.  (1)

• primarily caused by dermatophytes
• infectious fungi that feed on the keratin present in the skin, hair, and nails, that usually cause an inflammatory response at the site of infection
• yeasts and non-dermatophyte moulds can also cause onychomycosis, either alone or in combination with dermatophytes
• fungi are ubiquitous in the environment and are found in greater abundance in warm or damp areas that foster growth (e.g. public change rooms and showers of athletic facilities, sweaty shoes)
• for fungal infection to occur, a portal of entry to the nail unit has to exist
• usually occurs when there is trauma (i.e. injury) to the seal or space between the nail bed and nail plate
• trauma (i.e. nail deformity) can also occur from long-term wear of ill-fitting or tight shoes

Fungal nail infection may occur as a primary event or following other disease or damage to the nail. Fungal organisms affecting the nail may be divided into the following:

• dermatophytes (Tinea, 85-90% of fungal nail infections)
• yeasts (Candida often involved in chronic paronychia)
• Non-dermatophyte moulds - a rare cause of nail infection (1)

It is frequently seen in:

• people with other nail problems (e.g., a history of nail trauma)
• immunocompromised persons (with diabetes, HIV infection, immunosuppressive medications)
• people with peripheral vascular insufficiency (2)

A survey carried out in 2761 patients revealed that concomitant tinea pedis (in 33%), tinea cruris (in 4%) and tinea capitis (in 0.5%) were seen in people with toenail onychomycosis (3).

Treating these infections may be difficult but appropriate treatment is important as spontaneous resolution does not occur. There may also be co-existent bacterial infection which will influence management.

• many people seek treatment for cosmetic purposes, but onychomycosis is an infectious condition, so it is critical that it is treated to prevent cross-contamination to family members, and secondary complications such as tinea pedis
• patients with onychomycosis report decreased quality of life and may restrict their activities because of embarrassment about the aesthetic appearance of their nails

Note that many nail problems can look like fungal infections, eg psoriasis or injury. Always send samples before starting long-term treatment, as only 45% of dermatology samples received are positive for fungal infections (4)

Key points (5):

• take nail clippings; start therapy only if infection is confirmed
• oral terbinafine is more effective than oral azole
• liver reactions 0.1 to 1% with oral antifungals
• if candida or non-dermatophyte infection is confirmed, use oral itraconazole
• topical nail lacquer is not as effective
• to prevent recurrence: apply weekly 1% topical antifungal cream to entire toe area
• children: seek specialist advice

• (1) Roberts DT, Taylor WD, Boyle J. Guidelines for treatment of onychomycosis. British Journal of Dermatology 2003;148:402–410
• (2) De Berker D. Fungal nail disease. NEJM 2009; 360:2108-2116
• (3) Jacek C et al. Factors influencing coexistence of toenail onychomycosis with tinea pedis and other dermatomycoses. Arch Dermatol. 2006;142:1279-1284
• (4) Public Health England 2017. Fungal skin and nail infections: Diagnosis and laboratory investigation - Quick reference guide for primary care.
• (5) Public Health England (June 2021). Managing common infections: guidance for primary care