Don’t panic, this happens to runners and is caused by the repetition of your foot sliding in your shoe with each step you take. This is simply bruising under the nail as a result of either shoes that are too tight and are crushing the toe as you land or shoes that are too big, allowing for your toe to bash the front of the shoe as it slides with every stride. Bruised toenails are preventable if you ensure that your shoes fit properly and are laced up well to retain your heel properly and firmly in the heel cup of the shoe. The bruised toenails should heal on its own, just make sure to keep it clean and avoid infection. If there is bleeding under nail, this can cause discomfort and may lead to a painful nail, in which case you will want to visit us to have it evaluated and treated. You will want the blood and pressure removed under the nail so that the nail has a chance to reattach itself to the nail bed and avoid losing the toenail altogether. Left on its own, the black and blue will grow out on its own in three to five months.