If you're reading this, it's probably not because you love toenail fungus. It it also probably not because you think black toenails are pretty. In fact, you probably think both are pretty gross and you would be right. But this bruised black toenails and toenail fungus joining the party is mostly preventable. All runners should understand the circumstances that can put you at risk of getting a fungus infection in the nail which runners call "toenail fungus," or which doctors call "onychomycosis." It is often the fungus that actually causes the skin infection called athlete's foot. It's very, very common. Fungus is all over the place! Don't freak out, but it's probably in your shoes right now! Whether or not the fungal spores and fungal filaments will cause an infection on your feet, just depends upon the circumstances that you set up as a runner that actually allow it to get in and cause real trouble. How can a bruised toenail from running cause toenail fungus? Well, that's what we're talking about today on the Doc On The Run podcast.