A pooling of blood under the toenail, caused by the toe rubbing or hitting the top of your shoe. Often the toe will throb with the pressure of the blood.
Remedies: To relieve the pressure, you need to make a hole in the nail and drain the blood. Either heat the tip of a small, straightened paper clip and use it to burn through the nail until a drop of blood comes out, or sterilize the tip of a 1/16-inch drill bit with heat or alcohol and, by spinning the instrument between your finger and thumb, drill a hole in the nail. Stick your foot in a pan of water until all the blood comes out. (If you’re squeamish about doing this, see a sportsoriented physician.) Apply an antibacterial cream. Relieve inflammation with ice and anti-inflammatories.
If your black toenail isn’t painful, you don’t have to drain the blood. Lubricate with antifungal cream and cover it with a bandage. But monitor the nail, as it will probably loosen and fall offover the next few months. When it gets loose, carefully pull it off and continue to apply the antifungal cream. In the meantime, buy “a pair of running shoes with more room in the toe box.”
Excerpt From: Burfoot, Amby. “Runner's World Complete Book of Running.” Rodale, 2009. iBooks.