It could be ecchymosis. That's the medical term for a type of bruise. This dark purple spot forms on your skin when blood leaks out of your blood vessels into the top layer of your skin. It's usually from an injury, and it’s 1/2 inch long or bigger. A bruise or two on your arms or legs is usually nothing to worry about.

Ecchymosis, also known as a bruise, refers to the blue or purple skin discoloration that occurs as a result of rupture of blood vessels under the skin. Oftentimes, pain and tenderness accompany the discoloration.