Toenail fungus (onychomycosis) is caused by a group of fungi known as dermophytes. This group thrives on skin and on keratin, the main component of hair and nails. The fungus gets under the nail and begins to grow, damaging the nail so it discolors, becoming white, brown or yellow. Eventually, the nail might thicken, harden, become brittle and even fall off.
Nail fungus is usually harmless. But many people find discolored or thickened nails unpleasant to look at and want to get rid of the fungus as soon as possible. Fungal nail infections can also spread, and may infect other people. Regardless of the treatment you choose, it will take a while until the nail looks normal again. It’s especially important to be patient where toenails are concerned. It can take a year for a healthy big toenail to grow back. Nail fungus can sometimes be very persistent despite treatment. It can also come back after successful treatment.
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 A common outdated name that may still be reported by medical laboratories is Trichophyton mentagrophytes for T. interdigitale.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.
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.