How Do I Know Whether It's a Fungal Nail Infection or Something Else?

Medically Reviewed by Stephanie S. Gardner, MD on November 12, 2020

If your toenails are cracked, discolored, thicker than they should be or painful, you may wonder if you have a fungal nail infection. Although there are other problems that can affect what your nails look or feel like, a fungal infection is a common culprit.

Fungus is the cause of up to half of all nail infections. It’s very common among adults 60 and older -- about 3 out of 4 seniors have the problem, while only 1 of 5 younger adults are affected.

You can get a fungal nail infection on your fingernail as well, but it’s much more likely to show up on your toenails.

If you have type 2 diabetes, you should take nail fungus very seriously. Toenail fungus is twice as common in diabetic feet, and severe cases of it along with complications can lead to amputations. Always see your doctor if you’re diabetic and you notice any problem with your nails.

Other Nail Problems

These are less common than fungal nail infections, and they may have different signs and symptoms. They include:

Ingrown toenails, which hurt where the toenail grows into the skin, but the nail often appears normal.

Infections caused by bacteria, which can make the nail appear thick and hard, aor sometimes green. The skin around the nail and cuticle can look red and swollen.

Melanoma (the most dangerous kind of skin cancer). It’s very rare, but it happens and it may show up beneath a nail as a dark streak.

Fungal Nail Infection Symptoms

Because the toes and feet are often exposed to damp, warm areas, where the infection is spread, fungal nail infections affect the toes more than the fingers. Your feet are also more likely to be exposed to fungal infections if you:

  • Spend time at swimming pools
  • Walk around a lot in locker rooms
  • Wear the same pair of damp, sweaty sneakers all the time
  • Injure your toenail

At first, you may have no outward symptoms. But over time, your nails may:

  • Have white spots appear on the surface
  • Turn white, yellow, green or brown
  • Grow thicker than normal or, in some cases, thinner than normal
  • Become brittle, with broken or jagged edges
  • Change shape, curling up or down
  • Lift off of the nail bed
  • Smell bad
  • Cause you pain

When to See Your Doctor

Anytime you think you have a fungal nail infection, or any nail problem, and treating it at home doesn’t help, see your doctor or podiatrist (foot doctor). The sooner you go, the sooner your doctor can help.

Fungal nail infections can get worse over time. See your doctor if you notice your nail has turned brown or black, if it suddenly hurts, or if it pulls away from the nail bed.

If you have diabetes and you notice that the look of your toenails has changed even a little, see your doctor right away to prevent the problem from getting worse.

What Tests Might Be Done

Your doctor may be able to tell that you have a fungal nail infection just by looking at your toes or your fingers. But they may do some tests to be sure.

They may decide to take a sample of your nails. The clippings can be tested to see if fungus is in them.

If you do have nail fungus, you and your doctor will decide what treatment is best for you.


The best thing to do is avoid getting nail fungus in the first place. It’s worth the extra bit of time and effort to keep them fungus-free:

  • Keep your hands and feet clean and dry.
  • Keep your nails trimmed short. Cut your toenails straight across.
  • Don’t walk barefoot in locker rooms or on pool decks.
  • Change your socks and shoes when your feet get sweaty.
  • Have more than one pair of sneakers so your sweaty pair can dry out before you wear them again.

Show Sources


Centers for Disease Control and Prevention: “Fungal nail infections.”

Journal of the American Academy of Dermatology: “A large-scale North American study of fungal isolates from nails: The frequency of onychomycosis, fungal distribution, and antifungal susceptibility patterns.”

American Orthopaedic Foot & Ankle Society: “Toenail fungus,” “Ingrown toenails,” “Nails.”

American Academy of Dermatology: “Caring for nail infections.”

American Academy of Family Physicians: “Paronychia,” “Fungal nail infections.”

American Podiatric Medical Association: “Toenail fungus.”

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