If you notice a toenail becoming discolored and turning black, it's often due to injury that causes a bruise called a subungual hematoma . There can be other reasons for discoloration, however, and black toenail can be painful. This article will discuss black toenail, including what can cause it, what to do about it, and if you should call your healthcare provider. Photographer, Basak Gurbuz Derman / Getty Images Symptoms of Black Toenail The most common symptom of black toenail is exactly that—the nail appears black, which is usually due to blood collecting underneath the nail. However, the discoloration can also be reddish, purplish, or brownish. Other symptoms include: Pain Nail separates from nail bed over time Thickening and splitting of the nail If the area becomes infected, you may note: Swelling Odor Redness Discharge Some nail discoloration appears as striations, or lines, in the nail that are usually ver...