What is Toenail Fungus?

Over 46,000,000 Americans suffer from Nail Fungus ( Onychomycosis ) and 4,000,000 new cases are diagnosed each year.

Andrew Stills
25 July 2019
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Nail fungus (scientific name onychomycosis [on-ih-koh-my-KOH-sis]), is a common condition that usually first appears as a white or yellow spot under the tip of the fingernail or toenail. As the fungus deepens, it may cause the nail to discolor, thicken, and crumble at the edge. An infection may spread to multiple nails, and oftentimes, it may occur alongside of a skin fungus such as athlete’s foot (tinea pedis).

Fungal infection can vary in degree, calling for different levels and types of treatment. Cases that cause neither pain nor discomfort may require no special treatment at all. Those, by contrast, which produce symptoms such as pain or a thickened nail may require certain types of self-care and/or medication.

Even once they have been successfully eradicated, unfortunately, fungal nail infections are likely to recur. Certain preventive measures can, however, reduce the chance of re-infection.


Fungal nail infections occur when fungal organisms (fungi) found naturally in, on, or under the nail overpopulate. The fungi that most commonly produce nail infection are called dermatophyte. Other fungi, however, such as yeast and molds, can likewise cause infection.

A variety of factors can contribute to the overgrowth of fungi naturally present in your body, leading to infection. Among the most significant are temperature and moisture. Because fungi thrive in warm, moist environments, areas of the body that are regularly covered and warm offer breeding grounds for fungi. Hence nail fungus more commonly affects toenails than fingernails.

The same fungi that cause nail infection may also cause jock itch, athlete’s foot, and ringworm. One type of fungal infection may therefore lead to another. Athlete’s foot (foot fungus), for example, can spread to the nails, causing toenail infection. Fungal infections can also be communicated from one person to another.

Fungal nail infection can develop in persons of any age, but adults over the age of 65 are particularly susceptible due in part to the drier, thicker, brittler condition of aging nails. Cracks and chips provide the means whereby fungi may more easily enter, embed themselves, and overpopulate.

Other factors that affect the risk of infection include reduced blood circulation to the feet and a weakened immune system. Conditions such as diabetes, therefore, may particularly increase risk.

Generally speaking, the following factors increase the likelihood of developing a fungal nail infection:

  • age, particularly if over 65
  • a weakened immune system
  • a condition that causes poor circulation, such as diabetes
  • nail injury or damage
  • skin injury or damage near the nail, or a skin condition such as psoriasis
  • exposure to moisture for an extended time
  • occurrence of nail fungus among family members


Certain behaviors also increase the risk of nail infection, including but not limited to:

  • wearing artificial nails
  • walking barefoot in damp communal areas, such as gyms and shower rooms
  • swimming in a public swimming pool
  • wearing closed-toe shoes, such as tennis shoes or boots
  • frequenting a nail salon that fails to sanitize emery boards and nail clippers regularly and thoroughly

Simple lifestyle practices can help prevent fungal nail infection. The first and most important preventive measure is to keep your nails trimmed and clean.

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