Other risk factors include perspiring heavily, being in a humid or moist environment, psoriasis, wearing socks and shoes that hinder ventilation and do not absorb perspiration, going barefoot in damp public places such as swimming pools, gyms and shower rooms, having athletes foot (tinea pedis), minor skin or nail injury, damaged nail, or other infection, and having diabetes, circulation problems, which may also lead to lower peripheral temperatures on hands and feet, or a weakened immune system. Diagnosis
The diagnosis is generally suspected based on the appearance and confirmed by laboratory testing. The four main tests are a potassium hydroxide smear, culture, histology examination, and polymerase chain reaction. The sample examined is generally nail scrapings or clippings. These being from as far up the nail as possible.Nail plate biopsy with periodic acid-Schiff stain appear more useful than culture or direct KOH examination. To reliably identify nondermatophyte molds, several samples may be necessary. Classification
There are five classic types of onychomycosis:
Distal subungual onychomycosis is the most common form of tinea unguium and is usually caused by Trichophyton rubrum, which invades the nail bed and the underside of the nail plate. White superficial onychomycosis (WSO) is caused by fungal invasion of the superficial layers of the nail plate to form "white islands" on the plate. It accounts for around 10 percent of onychomycosis cases. In some cases, WSO is a misdiagnosis of "keratins granulations" which are not a fungus, but a reaction to nail polish that can cause the nails to have a chalky white appearance.
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 A common outdated name that may still be reported by medical laboratories is Trichophyton mentagrophytes for T. interdigitale.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. Other
Other causative pathogens include Candida and nondermatophytic molds, in particular members of the mold genus Scytalidium (name recently changed to Neoscytalidium), Scopulariopsis, and Aspergillus. Candida species mainly cause fingernail onychomycosis in people whose hands are often submerged in water. Scytalidium mainly affects people in the tropics, though it persists if they later move to areas of temperate climate. Other molds more commonly affect people older than 60 years, and their presence in the nail reflects a slight weakening in the nails ability to defend itself against fungal invasion. Nail injury and nail psoriasis can cause damaged toenails to become thick, discolored & brittle. Risk factors
Advancing age (usually over the age of 60) is the most common risk factor for onychomycosis due to diminished blood circulation, longer exposure to fungi, nails which grow more slowly and thicken, and reduced immune function increasing susceptibility to infection. Nail fungus tends to affect men more often than women and is associated with a family history of this infection.