Blood under the toenail is a common ailment for those used to strenuous exercise on the courts and other athletes who wear shoes and socks. Every time your foot moves forward, it bangs itself against the top front and side of the shoe and the feet may also swell when running or walking. The swelling in turn is compressed by tight socks and shoes and the pressure may damage the toenail bed leading to ingrown nails and blisters or blood under the nail.
The nail is usually swollen and slightly raised due to the blood underneath and you could wait for a day to see if it will subside on its own. If it is still painful after a day and the nail is slightly raised the best thing to do would be to see a doctor to get the fluid drained out. The fluid can be drained out at home, but must be done with care as it may damage the whole toe. Soak your feet in warm water with a handful of salt and half a lime squeezed into it. Make sure the nail and surrounding areas are thoroughly clean before patting the foot and nail dry. If the swollen area is near the edge of the nail, sanitize the area with alcohol, sterilize a needle and try to pierce the blister. Drain out all the fluid and apply an antibiotic cream. If the blister is not at the edge of the nail, you will have to drill through the nail to drain the excess fluid. Sterilize a brand new paper clip over a flame and pierce through the nail while it is still glowing and hot. Pierce just enough to make a puncture and press the nail with your fingers to let the fluid out. Use alcohol to sanitize the area and then apply an antibiotic cream. Wear open sandals for a week or two and allow the nail to heal on its own by keeping it dry and applying the cream regularly. If the toe becomes red, it still hurts or the swelling does not subside, you must consult a doctor immediately. Infection may set in and may infect the blood anytime causing gangrene, especially if you are diabetic. You will eventually lose the toenail and a new healthy nail will grow beneath it in about three months. In the mean time you may use a dark shade of nail polish over it to cover it up. Preventive measures involve wearing the correct shoe size and lacing your shoes up properly. Ensure that your heels do not slide to the front and bang against the top of the shoe.