While you're running, the feet bears the brunt of the work. When you factor in the pounding the feet take during a run, you can see why they are prone to injuries. Many runners complain of toenail pain following a long-distance run, and it's not uncommon for runners to lose a toenail every now and then—but don't worry, it grows back.
Ingrown toenails result when the edges of the toenail turn downward and grow into the soft tissue of the toe. This can lead to infection because the spot where the toenail is growing into the toe is like an open wound, and bacteria can get in there and cause problems.
Ingrown toenails are most commonly a result of not trimming your toenails properly. Avoid trimming the nail too short, as it has a tendency to grow into the soft part of the skin on the edges when it begins to regrow. A toenail that is more rounded also has a tendency to grow into the toe because there are no defined edges.
Shoes that are too small can cause the toenail to be pressed downward into the toe, and this could guide the direction in which the nail grows. Running and putting a lot of pressure on the feet and toes can also cause the toenails to grow into the toe.
Black toenails result from running in shoes that are too small or from the increased blood flow underneath the toenail. If your shoes or socks are too tight, the constant rubbing while running of your toe against the end of the shoe or sock will cause friction, resulting in a bruise or blackness under the toenail.
Black toenails can also be caused by the pressure of the blood forced into the toes as you run. With each stride, your foot comes forward, and blood flows forward in your foot, accumulating in your toe. This can lead to the pooling of blood underneath your toenail.
Warmer weather can also increase your chances of suffering from black toenails while running, since your feet tend to swell more in the heat.
Padding your toes or placing small amounts of cotton underneath your toenail where it is growing into the nailbed can be effective to help combat ingrown toenails. Additionally, changing shoes and resting the injured foot can help keep the ingrown toenail from getting worse.
To help heal a black toenail, rest and elevation will help reduce the blood flow to the area. You may choose to apply ice to your toe to decrease the blood flow and reduce the swelling.
Consider changing running shoes, selecting a pair with more toe room, before running again. You can wrap padding or bandages around the injured toe prior to running to help reduce the friction.
To prevent ingrown toenails, keep your toenails short enough so they won't rub against your shoes or socks while running, but long enough that you don't risk the edge of the nail growing into the flesh of your toe. You should also cut them square, so there is a defined edge to your nail.