A dermatologist has warned that a specific mark on your nail could be a sign of a serious health problem – so it's important ...

Dermatology Nursing. 2007;19(1):83-84. Athletes may develop sports-related subungual hematomas. Repeated trauma to the nail bed occurs each time the toe contacts the inside of the sneaker.

This may be a sign of a rare type of skin cancer, Subungual Melanoma. Although this is rare, it is a serious type of skin cancer, and if anyone notices it, they should immediately reach the hospital.