Injuries that lead to bleeding under the affected area of the skin typically cause discoloration of the skin in the area. Bruise is an injury to the skin causing blood vessels to rupture and the discoloration of tissue due to the presence of red blood cells. Petechia is a small red or purple spot on the body caused by a minor hemorrhage. Ecchymosis is a purplish patch under the mucous membranes or under the skin. Petechia, bruises, or ecchymoses may appear suddenly or after a minimal injury.