Toenail fungus is a fungal infection called onychomycosis. Tinea unguium is another name for it.
It’s an overgrowth of fungi that are often found on your body together with other bacteria. You can get the fungi from someone else too, like at a nail salon ifthe tools aren’t properly sterilized. It’s the same fungi that cause ringworm, jock itch, or athlete’s foot.
The problematic infection happens when the fungi get in through the cracks in your toenails and start to overpopulate in, on, or under the nail. It just loves warm, moist environments and often finds that in your toenail, especially when you wear shoes. And it’s even happier if you’re active and sweat in your sports shoes.