What Causes Toenail Fungus
Toenail fungus rarely comes from one dramatic event. It usually takes three things at once: an already-common fungus, an environment it likes, and a small opening to get under the nail. Most people who get it aren’t doing anything wrong; they’re just unlucky with timing and footwear.
The fungus itself is common and hard to avoid entirely
Most nail fungus is caused by dermatophytes, the same family of fungi behind athlete’s foot and ringworm. They live in soil, on surfaces, and on skin in general, and they’re everywhere — gym floors, pool decks, hotel carpets, your own bathmat. You can’t sterilise your way out of ever encountering them; the goal is making it hard for them to take hold, not making contact zero.
Warm, damp, enclosed shoes are the main accelerant
Fungus thrives in warmth and moisture. Feet inside closed shoes for hours a day, especially if they sweat, create close to ideal conditions. This is why toenail fungus is so much more common than fingernail fungus — fingers aren’t sealed into a damp, dark environment for eight hours a day the way feet often are.
A way in: injury, tight shoes, or athlete’s foot
An intact, healthy nail is a reasonably good barrier. Fungus usually gets under it through:
- A small trauma — stubbing a toe, tight shoes that press the nail against skin, or repetitive pressure from running.
- Athlete’s foot left untreated — the same fungus on the skin can spread to the nail, which is why treating skin infections promptly matters.
- A tiny separation between the nail and nail bed, sometimes from something as minor as a too-aggressive pedicure.
Why some people get it and others don’t
Exposure and opportunity explain part of it, but a few things clearly raise the odds:
- Age — nails grow more slowly and circulation is often reduced, both of which make an infection easier to establish and slower to clear.
- Diabetes or poor circulation — reduced blood flow to the feet weakens the local immune response. Diabetes can also dull feeling in the feet, so a thickening nail, or a small cut beside it, can go unnoticed for weeks; this explainer on how high blood sugar damages the nerves in your feet covers why a quick daily foot check matters so much.
- Excess sweating (hyperhidrosis) — more moisture, longer.
- Shared damp spaces — gym showers, pool decks, communal changing rooms, walked barefoot.
- A family history — some people appear to be more genetically susceptible.
What actually lowers the odds
None of this is about blame, but a few habits genuinely help: keeping feet dry, changing socks daily, rotating shoes so each pair gets a full day to dry out, and not walking barefoot on wet communal floors. We go through the at-home side of prevention and care in more depth in home remedies for nail fungus: which ones actually work.
Frequently Asked Questions
Is toenail fungus caused by poor hygiene?
Not really. Plenty of people with careful foot hygiene still get it, because the main drivers are warmth, moisture, and an opening in the nail — not dirt.
Can you get nail fungus from a nail salon?
Yes, if tools aren’t properly disinfected between clients. Salons using single-use files and disinfected metal tools are much lower risk.
Does sweating a lot make you more prone to nail fungus?
It’s a real contributing factor, since it keeps the inside of the shoe consistently damp — the environment fungus prefers.
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