Dermatophytes — fungus that grows on the skin, hair and nails but don’t penetrate tissues of the body. Athlete’s foot or Trichophyton rubrum is the most common dermatophyte and can actually infect the toenails. Infection can also begin by touching objects that have dermatophytes on them, such as nail clippers, nail files, socks, shoes, shower floors, etc. Dermatophytes are the cause of most fungal toenail infections.
Fungus can infect the skin and nails of your feet. A fungal infection of the skin is also known as Athlete’s Foot, which causes itching, burning, and flaking. This infection can spread to the toenails if it’s not treated. Both types of foot fungus are extremely contagious, both in your own body as well as to other people through contact. Therefore, it’s essential to treat the infection and prevent its recurrence.
The most common symptom of a fungal nail infection is the nail becoming thickened and discoloured: white, black, yellow or green. As the infection progresses the nail can become brittle, with pieces breaking off or coming away from the toe or finger completely. If left untreated, the skin underneath and around the nail can become inflamed and painful. There may also be white or yellow patches on the nailbed or scaly skin next to the nail,[6] and a foul smell.[7] There is usually no pain or other bodily symptoms, unless the disease is severe.[8] People with onychomycosis may experience significant psychosocial problems due to the appearance of the nail, particularly when fingers – which are always visible – rather than toenails are affected.[9]
If you notice any redness, increased swelling, bleeding,or if your infection is not clearing up, see your health care professional. If a bacterial infection is also occurring, an antibiotic pill may be necessary. If you have fungal nail involvement, are diabetic, or have a compromised immune system, you should also see your physician for treatment.

If the diagnosis is uncertain, direct microscopy of a potassium hydroxide preparation of a skin scraping (known as a KOH test) can confirm the diagnosis of athlete's foot and help rule out other possible causes, such as candidiasis, pitted keratolysis, erythrasma, contact dermatitis, eczema, or psoriasis.[13][23][27] Dermatophytes known to cause athlete's foot will demonstrate multiple septate branching hyphae on microscopy.[13]

Trichophyton rubrum is the most common dermatophyte involved in onychomycosis. Other dermatophytes that may be involved are T. interdigitale, Epidermophyton floccosum, T. violaceum, Microsporum gypseum, T. tonsurans, and T. soudanense. A common outdated name that may still be reported by medical laboratories is Trichophyton mentagrophytes for T. interdigitale. The name T. mentagrophytes is now restricted to the agent of favus skin infection of the mouse; though this fungus may be transmitted from mice and their danders to humans, it generally infects skin and not nails.
If the fungal infection has spread to the toenails, the nails must also be treated to avoid reinfection of the feet. Often, the nails are initially ignored only to find the athlete's foot keeps recurring. It is important to treat all of the visible fungus at the same time. Effective nail fungus treatment may be more intensive and require prolonged courses (three to four months) of oral antifungal medications.
Infected nails are usually thicker than normal and could be warped or oddly shaped. They can break easily. Nails with fungus might look yellow. Sometimes a white dot shows up on the nail and then gets bigger. When fungus builds up under your nail, it can loosen and even separate the nail from the bed. The fungus can also spread to the skin around your nail.
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