You have an ingrown toenail (the side of your nail grows into the skin). You've picked up a fungus, which you can get if you walk barefoot in common areas like a gym shower or locker room.

You can get toenail fungus from a bad pedicure, athlete’s foot from the gym shower, or—one of the most painful—an ingrown toenail from, well, a number of different things.

In addition to the symptoms of an ingrown nail, a paronychia can also cause warmth, pain and even buildup and drainage of pus. Ingrown nails are common, affecting 2% to 5% of the population annually.