Nail fungus is a fungal infection of the nails. A recent review of nail fungus surveys in European and American populations found an average prevalence of 4.3%. Tinea capitis can cause pain and discomfort, and can affect the quality of life of patients, impairing their psychological and physical health. Nail disease can lead to impaired or lost tactile function, while toenail disease hinders walking, movement, and comfort in shoes. Patients who do not receive treatment can transmit the disease to other family members and may contaminate public areas. Fungal infections of the nail can be chronic in course and resistant to treatment, with 16-25% of patients not cured by available treatments. To date, the infection is not known to clear spontaneously. Australian dermatologists Samantha Eisman and Professor Rodney Sinclair have published a review detailing the evidence-based diagnosis and management of onychomycosis. The review was published in the March 2014 issue of BMJ and the main points are compiled below. What is the etiology of onychomycosis? Tinea capitis is often caused by dermatophytic fungal infections and consists of three main species of fungi that can cause skin disease in humans and animals, namely, Microsporum spp. Dermatophyte infections of the nail are called onychomycosis. About 90% of cases are caused by Trichophyton rubrum, followed by mixed infections with Trichophyton interdigitalis and Trichophyton spp. Tinea capitis can also be caused by molds and yeasts other than dermatophytes, commonly Candida albicans. The distribution of these pathogens depends on geography, climate and migration. Who is at risk for infection? Nail fungus is a multifactorial disease. The fungus is ubiquitous and once the nail is damaged, there is an increased risk of infection. Diabetes is an independent risk factor, with 1/3 of people with diabetes being affected. A multicenter survey showed that diabetic patients were twice as likely to develop onychomycosis as non-diabetic patients. In diabetic patients, the diseased nail can damage the surrounding skin and may go unnoticed because of sensory neuropathy, leaving the patient vulnerable to osteomyelitis, gangrene and diabetic foot. Ageing is another risk factor, and in the elderly (age >70 years), the nail can damage the skin, leading to invasion by bacteria or other pathogens that can cause cellulitis. Genetics is also considered a risk factor, as Trichophyton rubrum infection has a familial autosomal dominant predisposition. Distal lateral onychomycosis caused by Trichophyton rubrum has a familial predisposition and is not associated with transmission between family members. In a multicenter study, patients with psoriasis were 56% more likely to develop onychomycosis than non-psoriatic patients of the same age and sex, and the prevalence of onychomycosis of the foot was 13%. In an epidemiologic study with 500 participants, the prevalence of onychomycosis in HIV-infected patients was 23.2% and was associated with a CD4 count of 370/mm3. In a large case series of onychomycosis, patients who smoked 2 or more packs per day accounted for 83.3% and nonsmokers 14.8%, with peripheral arterial disease being another confounding risk factor. Reported extrinsic risk factors included increased physical activity, increased work in humid environments, ill-fitting shoes, public swimming pools, work exposure to chemicals, barefoot walking, and nail biting. Prevalence also depends on occupation (athletes), climate, living environment, and frequency of travel. What are the clinical signs of onychomycosis? Tinea capitis can affect a single nail or, in exceptional cases, all nails. Toenails are 7 times more likely to be infected than nails. The first and fifth toenails are the most frequently affected, often secondary to tinea pedis. In contrast, nail infections are often associated with tinea corporis or tinea capitis and are more often unilateral.