Black toenail

1. Origin of Black Toenail
A common runner’s issue, “black toenail,” is usually caused by bleeding under the nail. During long runs, if the toe box is too tight or the foot slides back and forth inside the shoe, the toes repeatedly hit the front, breaking tiny blood vessels under the nail. The accumulated blood makes the nail appear black or dark purple. Downhill running, long distances, longer toes, or nails cut too long increase the risk. In short, it’s the result of repeated impact and pressure.

2. Warning Signs: When to Pay Attention Typical signs include:

• Toenail color darkening or turning black after a run

• Dull pain or pressure under the nail, discomfort when pressed

• Severe cases may loosen the nail, eventually causing it to fall off

• Early stages may feel like mild stinging, with discoloration appearing days later If pain is obvious or pressure under the nail is strong, bleeding is usually significant.

3. Prevention Before Exercise Key points: Space, Stability, Trimming.

• Toe box space: Ensure enough room in the front of running shoes, especially for long runs or downhill.

• Fix foot position: Use proper lacing to lock the heel and reduce sliding.

• Trim nails: Cut toenails short and flat before running to avoid hitting the shoe upper or extra pressure.

Summary: Black toenails are not a badge of honor—they’re just shoes and toes fighting. Proper space and fixation can prevent most cases.