Symptoms and causes

Symptoms

You may have nail fungus if one or more of your nails are:

  • Thickened
  • Whitish to yellow-brown discoloration
  • Brittle, crumbly or ragged
  • Distorted in shape
  • A dark color, caused by debris building up under your nail
  • Smellling slightly foul

Nail fungus can affect fingernails, but it's more common in toenails.

When to see a doctor

You may want to see a physician if self-care steps haven't helped and the nail becomes increasingly discolored, thickened or deformed. Also see a doctor if you have diabetes and think you're developing nail fungus.

Causes

Fungal nail infections are caused by various fungal organisms (fungi). The most common cause is a type of fungus called dermatophyte. Yeast and molds also can cause nail infections.

Fungal nail infection can develop in people at any age, but it's more common in older adults. As the nail ages, it can become brittle and dry. The resulting cracks in the nails allow fungi to enter. Other factors — such as reduced blood circulation to the feet and a weakened immune system — also may play a role.

Toenail fungal infection can start from athlete's foot (foot fungus), and it can spread from one nail to another. But it is uncommon to get an infection from someone else.

Risk factors

Factors that can increase your risk of developing nail fungus include:

  • Being older, owing to reduced blood flow, more years of exposure to fungi and slower growing nails
  • Sweating heavily
  • Having a history of athlete's foot
  • Walking barefoot in damp communal areas, such as swimming pools, gyms and shower rooms
  • Having a minor skin or nail injury or a skin condition, such as psoriasis
  • Having diabetes, circulation problems or a weakened immune system

Complications

A severe case of nail fungus can be painful and may cause permanent damage to your nails. And it may lead to other serious infections that spread beyond your feet if you have a suppressed immune system due to medication, diabetes or other conditions.

If you have diabetes, you may have reduced blood circulation and nerve supply in your feet. You're also at greater risk of a bacterial skin infection (cellulitis). So any relatively minor injury to your feet — including a nail fungal infection — can lead to a more serious complication. See your doctor if you have diabetes and think you're developing nail fungus.

July 26, 2017
References
  1. Onychomycosis. Merck Manual Professional Version. https://www.merckmanuals.com/professional/dermatologic-disorders/nail-disorders/onychomycosis. Accessed May 15, 2017.
  2. Goldstein AO, et al. Onychomycosis: Management. https://www.uptodate.com/contents/search. Accessed May 15, 2017.
  3. Toenail fungus. American Podiatric Medical Association. http://www.apma.org/Learn/FootHealth.cfm?ItemNumber=1523. Accessed May 15, 2017.
  4. Varade RS, et al. Cutaneous fungal infections in the elderly. Clinics in Geriatric Medicine. 2013;29:461.
  5. Gupta AK, et al. Improved efficacy in onychomycosis therapy. Clinics in Dermatology. 2013;31:555.
  6. Westerberg DP, et al. Onychomycosis: Current trends in diagnosis and treatment. American Family Physician. 2013;88:762.
  7. AskMayoExpert. Fungal nail infection (onychomycosis). Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2017.
  8. Nail care. Natural Medicines. https://naturalmedicines.therapeuticresearch.com/databases/medical-conditions/n/nail-care.aspx. Accessed May 17, 2017.
  9. Gibson LE (expert opinion). Mayo Clinic, Rochester, Minn. June 6, 2017.