Nail fungus is a common infection of the nail. It begins as a white or yellow-brown spot under the tip of your fingernail or toenail. As the fungal infection goes deeper, the nail may discolor, thicken and crumble at the edge. Nail fungus can affect several nails.

If your condition is mild and not bothering you, you may not need treatment. If your nail fungus is painful and has caused thickened nails, self-care steps and medications may help. But even if treatment is successful, nail fungus often comes back.

Nail fungus is also called onychomycosis (on-ih-koh-my-KOH-sis). When fungus infects the areas between your toes and the skin of your feet, it's called athlete's foot (tinea pedis).


Symptoms of nail fungus include a nail or nails that are:

  • Thickened
  • Discolored
  • Brittle, crumbly or ragged
  • Misshapen
  • Separated from the nail bed
  • Smelly

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

When to see a doctor

You may want to see a health care provider if self-care steps haven't helped and the nail becomes increasingly discolored, thickened or misshapen. Also talk with your health care provider if you have:

  • Diabetes and think you're developing nail fungus
  • Bleeding around the nails
  • Swelling or pain around the nails
  • Difficulty walking

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Mayo Clinic Minute: Health Precautions You Need to Know About Pedicures

Vivien Williams: There's nothing like getting pampered with a pedicure. But before you dip your toes in the water, check to be sure the spa is licensed properly.

Rachel Miest, M.D., Department of Dermatology, Mayo Clinic: Oftentimes, those licenses come with the appropriate education, and following the appropriate protocols for how to keep you safe and how to prevent infection.

Ms. Williams: Dr. Rachel Miest says bacterial and fungal are the two most common infections. To avoid them, she says, don't be afraid to ask to make sure the spa cleans all equipment between customers.

Dr. Miest: Even if all of the appropriate precautions are taken from a cleaning standpoint, bacteria, viruses, fungi ─ these things are everywhere.

Ms. Williams: To reduce your risk, Dr. Miest says don't shave 24 hours beforehand and don't have your cuticles cut.

Dr. Miest: Ask that they only either leave your cuticles alone or gently push them back but not to aggressively push them back or clip them because that cuticle is a very, very important seal.

Ms. Williams: For the Mayo Clinic News Network, I'm Vivien Williams.

Mayo Clinic Minute: Fingernails are clues to your health

Vivien Willliams: Your fingernails are clues to your overall health. Many people develop lines or ridges from the cuticle to the tip.

Rachel Miest, M.D., Department of Dermatology, Mayo Clinic: Those are actually completely fine and just a part of normal aging.

Ms. Williams: But Dr. Rachel Miest says there are other nail changes you should not ignore that may indicate …

Dr. Miest: liver problems, kidney problems, nutritional deficiencies …

Ms. Williams: And other issues. Here are six examples: No. 1 is pitting. This could be a sign of psoriasis. Two is clubbing. Clubbing happens when your oxygen is low and could be a sign of lung issues. Three is spooning. It can happen if you have iron-deficient anemia or liver disease. Four is called "a Beau's line." It's a horizontal line that indicates a previous injury or infection. Five is nail separation. This may happen as a result of injury, infection or a medication. And six is yellowing of the nails, which may be the result of chronic bronchitis.

For the Mayo Clinic News Network, I'm Vivien Williams.

Nail fungus is caused by various fungal organisms (fungi). The most common is a type called dermatophyte. Yeast, bacteria and molds also can cause nail infections. The discoloration from a bacterial infection tends to be green or black.

Fungal infection of the foot (athlete's foot) can spread to the nail, and a fungal infection of the nail can spread to the foot. You can also get the infection from contact with spaces where fungi can thrive, such as the floor tile in a gym shower or inside dark, sweaty, moist shoes.

Risk factors

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

  • Older age
  • Wearing shoes that make your feet sweat heavily
  • Having had athlete's foot in the past
  • Walking barefoot in damp public areas, such as swimming pools, gyms and shower rooms
  • Having a minor skin or nail injury
  • Having a skin condition that affects the nails, such as psoriasis
  • Having diabetes, blood flow problems or a weakened immune system


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.


The following habits can help prevent nail fungus or reinfections and athlete's foot, which can lead to nail fungus:

  • Keep your nails clean and dry. Wash your hands and feet regularly. Wash your hands after touching an infected nail. Dry well, apply an antifungal foot powder and moisturize your nails. Consider applying a nail hardener, which might help strengthen nails and cuticles.
  • Keep your nails trimmed. Cut nails straight across, smooth the edges with a file and file down thickened areas. Disinfect your nail clippers after each use. Letting your nails grow long creates more places for the fungus to grow.
  • Wear absorbent socks or change your socks throughout the day.
  • Choose shoes made of materials that breathe.
  • Discard old shoes or treat them with disinfectants or antifungal powders.
  • Wear footwear in pool areas and locker rooms.
  • Choose a nail salon that uses sterilized manicure tools for each customer. Or disinfect tools you use for home pedicures.
  • Give up nail polish and artificial nails.
  • If you have athlete's foot, treat it with an antifungal product.

May 15, 2024
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