A black patch suddenly appeared on the toenail.

One is to rule out whether the thumb has a recent history of trauma, trauma can cause ecchymosis under the nail, manifested as black mass or blood stasis; the other is active growth of melanin cells in the nail matrix, began to show a strip nevus under the nail, is also a kind of pigmented nevus, manifested as a strip. It is recommended that patients go to the hospital in time, clear the cause of treatment.