Black seed oil is extracted from the seeds of the annual flowering plant Nigella sativa, also referred to as black seed or black cumin, says Loretta Pratt, M.D., a dual board-certified internal medicine physician and dermatologist at Advanced Dermatology PC in Chadds Ford, Pennsylvania. Native to Southern Europe, North Africa and Southwest Asia, black seed oil is used to treat a wide range of illnesses, including cardiovascular disorders, diabetes and cancers, among others, due to one of its main components, thymoquinone. Black seed oil is most commonly used in food, typically as a spice or preservative.