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Symptoms and Signs of Fungal Nail Infection (Onychomycosis)

Doctor's Notes on Fungal Nail Infection (Onychomycosis)

Fungal nail infection is medically known as onychomycosis and refers to infections of the finer- or toenails by fungal organisms. In healthy people, fungal infections of the nails are most commonly caused by fungus that is caught from moist, wet areas, including communal showers or swimming pools. Inadequate sanitization of instruments used in nail salons is also a possible cause. Wearing tight-fitting, sweaty shoes while exercising with repetitive trauma to the toenails is also a risk factor for developing fungal nail infection.

Signs and symptoms of fungal nail infection include infection of the surrounding cuticle, elevation of the nail from the nail bed, a white powdery appearance to the nail, and thickening of the nails. Another possible associated symptom is discoloration of the nails.

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Medically Reviewed on 3/11/2019

Fungal Nail Infection (Onychomycosis) Symptoms

  • Fungal nail infection usually does not cause any symptoms (painless) unless the nail becomes so thick it causes pain when wearing shoes. People with fungal nail infection usually go to the doctor for cosmetic reasons, not because of physical pain or problems related to fungal nail infection.
  • As the nail thickens, however, fungal nail infection may interfere with standing, walking, and exercising.
  • Paresthesia (a sensation of pricking, tingling, or creeping on the skin having no objective cause and usually associated with injury or irritation of a nerve), pain, discomfort, and loss of agility (dexterity) may occur as the disease progresses. Loss of self-esteem, embarrassment, and social problems can also develop.
  • Severe cases of Candida infections can disfigure the fingertips and nails.

Symptoms or signs (appearances) of fungal nail infection based on subtype

Fungal nail infection is divided into subtypes that can be identified based on where the infection appears to be located relative to the structure of the nail.

  • In distal lateral subungual onychomycosis (DLSO), the nail plate is thick with a cloudy appearance (opaque), the nail bed underneath the nail thickens (becomes raised) and hardens (nail bed hyperkeratosis), and the nail separates from the bed underneath (onycholysis). The nail can be discolored and appear in a range from white to brown. The edge of the nail becomes severely eroded (ragged and brittle) and may become flaky (peeling).
  • In endonyx onychomycosis (EO), the nail plate has a milky white discoloration, but unlike DLSO, the nail does not separate from the bed (no onycholysis). The area under the nail (subungual area) does not thicken or harden (no hyperkeratosis).
  • White superficial onychomycosis (WSO) is usually confined to the toenails. Small white speckled or powdery-looking patches appear on the surface of the nail plate. The nail becomes rough and crumbles easily (crumbly nails).
  • In proximal subungual onychomycosis (PSO), an area of white spotting, streaking, or discoloration (leukonychia) develops near the nail fold and may extend to deeper layers of the nail. The nail plate becomes white near the cuticle and remains normal at the end.
  • In total dystrophic onychomycosis, the nail is thickened, opaque, and yellow-brown and/or greenish-brown to black. The entire nail plate and matrix are affected.
  • Yeast infection (Candida albicans), while affecting the nail, can appear with additional signs. Candidal infection can occur in the toenails and the fingernails but may also infect the tissue that surrounds the nail. The nail fold becomes inflamed (erythematous), or the nail plate separates from its bed (onycholysis). The nail bed thickens and hardens (nail bed hyperkeratosis), and inflammation of the nail fold is observed in chronic mucocutaneous disease (disease of mucous membrane and regular skin). The affected fingers or toes start to look rounded on the ends, like drumsticks, and, sometimes, the entire thickness of the nail becomes infected.
  • Some fungal infections may be associated with an odor described as a slightly foul odor or a "cheesy" odor. This odor may be due to chemicals (S-methyl thioesters) produced by bacteria that can colonize fungal-infected and other warm, damp areas.
Picture of fungal nail infection on the big toes
Picture of fungal nail infection on the big toes; SOURCE: CDC/Dr. Edwin P. Ewing, Jr.

Fungal Nail Infection (Onychomycosis) Causes

Fungal nail infection is caused by three main classes of organisms: fungi that infect hair, skin, and nails and feed on nail tissue (dermatophytes), yeasts, and non-dermatophyte molds. All three classes cause the very similar early and chronic symptoms or appearances, so the visual appearance of the infection may not reveal which class is responsible for the infection. Dermatophytes (including Epidermophyton, Microsporum, and Trichophyton species) are, by far, the most common causes of fungal nail infection worldwide. Yeasts cause 8% of infections, and non-dermatophyte molds cause 2% of fungal nail infections.

  • The dermatophyte Trichophyton rubrum is the most common fungus causing distal lateral subungual onychomycosis (DLSO) and proximal subungual onychomycosis (PSO).
  • The dermatophyte Trichophyton mentagrophytes commonly causes white superficial onychomycosis (WSO), and more rarely, WSO can be caused by species of non-dermatophyte molds.
  • The yeast Candida albicans is the most common cause of chronic mucocutaneous candidiasis (disease of mucous membrane and regular skin) of the nail.

Ringworm Treatment, Pictures, Causes, and Symptoms Slideshow

Ringworm Treatment, Pictures, Causes, and Symptoms Slideshow

Ringworm is a common fungal skin disorder otherwise known as "tinea" or dermatophytosis. It is caused by a fungus that can live on skin, surfaces like gym floors, and household items like towels, bedding, and clothes. While there are multiple forms of ringworm, the most common forms affect

  • the skin on the body
  • the scalp
  • the feet ("athlete's foot"), or
  • the groin ("jock itch").

Ringworm attacks dead tissues in places like the hair, nails, and leftover dandruff. But our bodies’ immune reactions and local bacterial infections enable ringworm to turn healthy, living skin red and itchy.


Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.