Also known by the Greek term “Onychomycosis,” most nail fungus infections are caused by dermatophyte fungi that feed on the keratin protein in the nail. Three specific clinical presentations of the disease have been identified as outlined below.
- Distal Subungal Onychomycosis (DSO) is the most common form of the disease. Sometimes also referred to as Distal/Lateral Onychomycosis, the dermatophyte fungus starts at the distal edge (the tip of the nail) or the side of the nail plate. The fungus advances towards the nail cuticle causing yellow and brown discoloration. As the fungus resides underneath the nail (a “subungal” position), if left to progress to an advanced stage the nail plate will start to separate from its bed. It is common for the nail to start to thicken and for debris to collect under the nail tip. Endonyx Onychomycosis (EO) is a variant of DSO where the fungi infect the nail plate directly via the skin. See toenail fungus pictures.
- White Superficial Onychomycosis (WSO) is the next most common form of infection. It starts on the external face of the nail plate and is associated with white or opaque patches or stains. Over time these patches darken and may also take on a yellowish or brownish color. As the fungus is more superficial than is the case with DSO, it is generally easier to treat with a topical antifungal treatment.
- Proximal Subungal Onychomycosis (PSO) is a rarer form of infection where the dermatophyte fungus invades from the cuticle end of the nail, specifically from under the proximal fold. It advances towards the tip of the nail causes a spreading discoloration. This is one of the most serious form of the disease which can cause the nail to detach entirely from the nail bed. Immunodeficient patients are particularly susceptible to PSO.
The diagram below illustrates locations of early stage DSO, WSO and PSO on the nail.
In addition to the above three forms of nail fungus, a fourth also exists. But it is not caused by a dermatophyte fungus, but rather by the Candida albicans yeast species. Known as Candidal Onychomycosis, it normally occurs in patients who are also suffering other symptoms of a Candida yeast infection. It is common for the the skin on either side of the nail to become inflamed. In fact in some cases, the skin is where the infection first starts, only later spreading to invade the nail. The nail surface can develop transverse groves, become convex and take on a yellow discoloration.
We cover different options for the treatment of Onychomycosis on other pages of this site. The page on nail fungus treatment, provides a summary chart of some of the most popular therapies including topical treatments such as Tineacide, Funginix and Zetaclear. And here’s more information on toenail fungus treatment.