Bluish-black toenails are usually dry blood accumulations beneath the nail plates that result from long-term repetitive trauma. This condition is frequently seen in distance runners, exercise walkers, and in those individuals involved in racquet sports. The toes involved are most often the second digits (next to the big toe) because of their being the longest. In most cases, these toes are painless but generally cause concern because of their progressively darkening appearance.
The cause of this nail condition is repetitive trauma secondary to shoe pressure. What happens is that when a person stops in walking or running, the undersurface of the athletic shoe grips the ground and forward motion is abruptly halted. However, the foot inside the shoe often continues for a short time period to slide forward until the toes jam into the end and upper portion of the shoe. The result of this repetitive traumatic jamming pressure against the toes is predictably a thickening of the nail plate with frequent bluish-black discoloration due to the accumulation of blood.
There are no effective treatments for this problem as long as the involved activity is continued. I recommend to patients that they check carefully their athletic shoes for a proper fit, consider the use of Band-Aids during the activity for added protection, and make sure that their nails are trimmed properly. On rare occasion, when discomfort is present and continued athletic participation is in jeopardy, the involved nail plate(s) can be removed. However, after all is said and done, these discolored nails and athletic participation seem to go hand in hand and in most cases, with no serious consequences to the participant.