Q: Why is my toenail “black”? A: A black toenail is usually caused by a blood blister underneath the nail. The collection of blood under the nail discolours it and in some cases can cause pressure and pain. If there is pain due to the increased pressure, your family doctor or podiatrist will need to drain the blood. The best way to prevent black toenails is to ensure that you have proper fitting shoes, meaning the toe box should be wide enough and the shoes long enough so that your toes don’t bump against the sides or end of the