Onychomycosis is a condition that may be caused by a number of potential pathogens. These can be categorized in three general classes of dermotophytes, Candida and nondermatophytic molds.

In temperate western countries, the fungi most commonly responsible for causing this condition are dermatophytes. In areas with a hot and humid climate, however, such as in the tropics and subtropics Candida and nondermatophytic molds are more frequently involved as the cause of the infection.

Dermatophytes

There are several dermatophytes that may be accountable for causing onychomycosis, although the most common is Trichophyton rubrum. In addition to this, some other dermatophytes that may play a role in some individuals are:

• Trichophyton interdigitale
• Epidermophyton floccosum
• Trichophyton violaceum
• Microsporum gypseum
• Trichophyton tonsurans
• Trichophyton soudanese

Medical laboratories occasionally refer to Trichophyton mentagrophytes as Trichophyton interdigitale, although this is outdated terminology and should be restriced to the favus skin infection agent in mice. This fungus can be transmitted to humans via mice and their excrement, although it usually produces a skin infection rather than affecting the nails.

Candida albicans

Candida albicans is primarily responsible for causing onychomycosis of the fingernail. It occurs most commonly to people whose hands area often submerged in water, such as swimmers and divers.

The infection usually affects the soft tissue surrounding the nails initially and then continues to cause a secondary infection to the nail plate after this has occurred.

Nondermatophytic molds

The mold generations that are most frequently known to lead to nail fungus are Scytalidium (also now known as Neoscytalidium), Scopulariopsis and Aspergillus.

In tropical and subtropical climates, Scyalidium is a common cause of onychomycosis and affects a large number of people. In addition, this infection is known to persist without treatment, even if affected individuals later relocate to areas with a more temperate climate.

Nondermatophytic molds are more likely to affect elderly people that are at least 60 years of age. This is often as a result of slight weakening in the nails ability to fight off infection, predisposing them to the condition.

Risk Factors

Whilst not directly causing onychomycosis, there are several factors that are associated with a higher risk of suffering from the condition.

Age is a strong risk factor of onychomycosis. This is thought to be due to decreased blood circulation and weakening of the nail’s defense against fungal infection and its ability to protect itself. In addition, elderly people’s nails tend to grow more slowly and are often thicker than the nails of people in the general population. Finally, it is likely that people of advanced age are more likely to be affected as they have been exposed to the fungi for a longer period of time.

Exposure to moist environments can also increase the probability that an individual will be affected by the conditions. This includes humid temperatures, as well as heavy perspiration that is secreted directly onto individuals skin.

Restricted ventilation to the area can also lead to risk of infection. This is particularly common for toenails, when individuals wear socks and shoes that do not allow the feet to breathe and often store perspiration to create a moist environment.

Additionally, the fungus can also be transmitted among humans that are affected. Neglecting to wear shoes in public places where contact with the fungus may occur such as swimming centers, gyms and shower rooms is likely to increase chance of infection.

Finally, some existing health conditions are associated with a higher risk of onychomycosis. These include psoriasis, athlete’s foot (also known as tinea pedis), damage to nails, diabetes, circulation problems and a weak immune system.