What does a black nail indicate?

A black nail is typically indicative of heavy bruising, known as a subungual hematoma, which occurs when there is trauma to the nail bed. This trauma causes blood to accumulate between the nail and the nail bed, leading to a dark discoloration under the nail. It is important to note that while other conditions can also affect nail color, the presence of a black nail specifically resulting from bruising is characterized by the trauma experienced.

In contrast, conditions like fungal infections usually cause discoloration that is different from the dark blood-related bruising seen with a black nail. Poor blood circulation might result in a bluish or purplish tint but not specifically black. Infections under the nail can lead to changes in color as well, but the typical presentation is not exclusively black as seen with bruising. Therefore, the characteristic of heavy bruising leading to a black nail clearly distinguishes it from other conditions.