There are four major types of fungal nail infections. They are named for the area where the fungal infection starts.
Distal subungual onychomycosis (DSO)
DSO is the most common type of fungal nail infection. It is caused by the same fungi that cause most cases of athlete’s foot (dermatophytes). DSO infects the skin under the end of the nail and in the nail. The infection starts at the end of the nail bed, and part of the nail often turns yellow or white.
White superficial onychomycosis (WSO)
WSO the second most common type of fungal nail infection, accounts for about 7% of all fungal nail infections.2 It can be easily treated. WSO affects the top layer of the nail, first forming white spots on the nail surface. Eventually the entire surface of the nail becomes covered with a crumbly, chalky powder.
Candida onychomycosis
Yeast infection of the nail, is uncommon but can affect the nail and the skin bordering the nail. This type of fungal infection is more common in fingernails than toenails. It may involve all of the nails at the same time and can cause the nail to separate from the nail bed. It invades weakened areas of the nail, which may become discolored white, green, or brownish, with an odd shape. The nail may look thicker than normal, and there may be signs of infection.
Proximal subungual onychomycosis (PSO)
PSO is caused by dermatophytes and accounts for about 3% of all fungal nail infections.