There are many signs of a nail fungus, however, not all the signs may necessarily mean that you actually have a nail fungus. The most common color that signifies a nail fungus is yellow nails, but blue or blackening nails tend to be misinterpreted as a sign of the nail fungus as well. Blue or black coloring are typically due to an injury to the nail that takes place beneath the toenail. The trauma causes a buildup of fluid and blood which is how the coloring comes about. For athletes, this is usually also a result of trauma from their shoes, which do not have enough space in the toe area of the shoe, causing a consistent trauma to the nail. The repeated stress to the front, side, and top of the toes in the shoe often results in blood blisters to come about under the toenail as a result.
If you are someone who suffers from black or blue nails make sure that address the issue as soon as possible. By avoiding tight fitting shoes and wearing ones that have more space in the toe area you can avoid the discomfort of the nails and allow a healthier nail to slowly grow back in.