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What Causes Toenail Fungus? Where It Comes From and Who Gets It

Toenail fungus doesn't come from being unclean. It comes from common fungi that love warm, damp places, and some people are more likely to pick it up than others. Here's how it happens.

· 6 min read · By the FungalNailTest.com team

Finding out you might have toenail fungus can feel a bit embarrassing, but it shouldn't. Fungal nail infections are common, especially in adults, and they have far more to do with warmth, moisture, age and small nail injuries than with how clean you are. Understanding where the fungus comes from can help you protect your other nails, the people you live with, and your nails after treatment.

What toenail fungus actually is

The medical name is onychomycosis: a fungal infection of the nail. The fungus lives in and under the hard nail plate, which is why it can be stubborn and slow to clear. Over time it can make the nail thick, discoloured (white, yellow or brown), brittle and crumbly, and sometimes lift it away from the skin underneath.

Which fungi cause it

Several kinds of fungi can infect nails:

  • Dermatophytes are the most common cause of toenail infections. They're the same group of fungi that causes athlete's foot and ringworm, and they feed on keratin, the protein that makes up skin, hair and nails.
  • Yeasts (such as Candida) more often affect fingernails, particularly in hands that are frequently wet.
  • Non-dermatophyte moulds cause a smaller share of infections, more often in nails that are already damaged.

The type matters to healthcare providers, because it can influence which treatment they consider. Depending on the test, a nail sample can help show whether fungus is present and, sometimes, what kind.

How fungus gets into a nail

The fungi that cause nail infections are all around us. According to the American Academy of Dermatology (AAD), you can develop nail fungus when fungi get into a tiny opening in or under the nail, or in the skin around it. Common ways that happens include:

  • Walking barefoot on floors where fungi thrive: pool decks, gym change rooms, public showers and shared bathrooms.
  • Athlete's foot. A fungal infection of the skin between the toes can spread into the nail. Mild athlete's foot is easy to mistake for dry skin.
  • Sharing items like towels, shoes, socks, or nail clippers and files that haven't been cleaned.
  • Close contact with someone who has nail fungus or athlete's foot, especially in the same household.
  • Feet that stay damp: sweaty socks, wet boots, or shoes that don't breathe.

Not everyone exposed to these fungi develops an infection. Whether you do depends on the condition of your nails and skin, how much time your feet spend warm and damp, and your overall health.

Why feet are a perfect target

Toenails are affected far more often than fingernails. Shoes and socks create the warm, dark, moist environment fungi love. Toenails also grow more slowly than fingernails, and take more knocks inside shoes, all of which can make them easier for fungus to settle in and harder to clear.

Canadian winters add a twist: long days in insulated boots can leave feet sweaty for hours, and shared change rooms at rinks, pools and gyms are part of everyday life for many families.

Who is more likely to get toenail fungus?

Anyone can develop toenail fungus, but the AAD and the Canadian Dermatology Association describe several factors that raise the chances:

Age

Nail fungus is much more common in adults than in children, and it becomes more common as we get older. Nails grow more slowly with age, and the body's ability to fight off infection changes too.

Nail and foot conditions

Health conditions

  • Diabetes, poor circulation or peripheral artery disease. If this applies to you, read toenail fungus and diabetes and involve a healthcare provider early.
  • A weakened immune system, for example from certain medications, cancer treatment or other conditions.

Habits and environment

  • Regularly walking barefoot in shared wet areas.
  • Tight or non-breathable shoes, or wearing the same damp pair day after day.
  • Sharing nail tools without disinfecting them.
  • Having family members who've had nail fungus.

Common myths about the cause

  • "It means I'm not clean." Not true. People with excellent hygiene get toenail fungus. Warmth, moisture and small openings in the nail matter far more.
  • "Nail polish causes it." Polish doesn't cause a fungal infection, though it can hide early changes and sometimes leave white marks of its own (see white spots on toenails).
  • "Every thick, yellow nail is fungus." Many discoloured nails turn out not to be fungal. Injury, psoriasis and other conditions can look very similar.

Knowing the cause starts with knowing it's fungus

Because so many nail problems look alike, the first step is confirming whether fungus is really there. That's where a test comes in. Our at-home kit uses qPCR DNA testing on a nail clipping you take yourself, and every result is reviewed by a licensed Canadian podiatrist with over 50 years of experience. Your report arrives 4–14 days after your sample reaches us, so you and your healthcare provider can decide on next steps with real information. See a sample report or learn how to read your results.

Once you know, the habits in our guide on how to prevent toenail fungus can help keep it from coming back.

Frequently asked questions

Is toenail fungus caused by poor hygiene?

No. Toenail fungus is caused by common fungi that thrive in warm, damp environments. People with very good hygiene can still get it. Keeping feet clean and dry helps lower the risk, but an infection isn't a sign that you're unclean.

Can athlete's foot turn into toenail fungus?

Yes. The fungi that cause athlete's foot can spread into a toenail, especially through small openings in or around the nail. Treating athlete's foot promptly is one of the simplest ways to lower your risk.

Why do older adults get toenail fungus more often?

Nail fungus becomes more common with age. Nails grow more slowly, circulation can be reduced, and the body's ability to fight infection changes, which makes it easier for fungus to take hold.

Can I get toenail fungus from a nail salon?

It's possible if tools like clippers and files aren't properly cleaned and disinfected between clients. Choosing a salon with good hygiene practices, or bringing your own tools, can lower the risk.

How do I know if my toenail problem is really caused by fungus?

Appearance alone isn't reliable, because injury, psoriasis and other conditions can look similar. A nail test, such as a qPCR DNA test of a nail clipping, can show whether fungal DNA is present. Share the result with a healthcare provider.

Sources

Important

This article is general information, not medical advice, and is not a substitute for a healthcare provider. Nail changes can have many causes. If you have diabetes, poor circulation, a weakened immune system, pain, swelling or signs of infection, see a healthcare provider promptly.

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