BOTH A BANE TO RUNNERS and – in some strange way – a badge of honour, the black toenail, or ‘subungual haematoma’, is actually blood collecting underneath your nail.
It can occur from acute or chronic injury, explains Dr Jordan Metzl, a sports medicine doctor at the Hospital for Special Surgery in New York City.
The chronic repetitive trauma can range from mild (think small, painless, black-and-blue discoloration beneath the nail) to severe (large, bloody blisters between nail and nail plate), adds podiatric surgeon Dr Jacqueline Sutera.
Other issues can cause discoloration, too, such as fungal infections, which can come with a smelly odour, and subungual melanoma, a type of skin cancer often causing a black or brown streak under your nail.
Loop in your doctor if you notice those…